As the Sabbath evening approached on Jan. 13, Ehud Barak paced the wide living-room floor of his home high above a street in north Tel Aviv, its walls lined with thousands of books on subjects ranging from philosophy and poetry to military strategy. Barak, the Israeli defense minister, is the most decorated soldier in the country’s history and one of its most experienced and controversial politicians. He has served as chief of the general staff for the Israel Defense Forces, interior minister, foreign minister and prime minister. He now faces, along with Prime Minister Benjamin Netanyahu and 12 other members of Israel’s inner security cabinet, the most important decision of his life — whether to launch a pre-emptive attack against Iran. We met in the late afternoon, and our conversation — the first of several over the next week — lasted for two and a half hours, long past nightfall. “This is not about some abstract concept,” Barak said as he gazed out at the lights of Tel Aviv, “but a genuine concern. The Iranians are, after all, a nation whose leaders have set themselves a strategic goal of wiping Israel off the map.”

When I mentioned to Barak the opinion voiced by the former Mossad chief Meir Dagan and the former chief of staff Gabi Ashkenazi — that the Iranian threat was not as imminent as he and Netanyahu have suggested and that a military strike would be catastrophic (and that they, Barak and Netanyahu, were cynically looking to score populist points at the expense of national security), Barak reacted with uncharacteristic anger. He and Netanyahu, he said, are responsible “in a very direct and concrete way for the existence of the State of Israel — indeed, for the future of the Jewish people.” As for the top-ranking military personnel with whom I’ve spoken who argued that an attack on Iran was either unnecessary or would be ineffective at this stage, Barak said: “It’s good to have diversity in thinking and for people to voice their opinions. But at the end of the day, when the military command looks up, it sees us — the minister of defense and the prime minister. When we look up, we see nothing but the sky above us.”

Netanyahu and Barak have both repeatedly stressed that a decision has not yet been made and that a deadline for making one has not been set. As we spoke, however, Barak laid out three categories of questions, which he characterized as “Israel’s ability to act,” “international legitimacy” and “necessity,” all of which require affirmative responses before a decision is made to attack:

1. Does Israel have the ability to cause severe damage to Iran’s nuclear sites and bring about a major delay in the Iranian nuclear project? And can the military and the Israeli people withstand the inevitable counterattack?

2. Does Israel have overt or tacit support, particularly from America, for carrying out an attack?

3. Have all other possibilities for the containment of Iran’s nuclear threat been exhausted, bringing Israel to the point of last resort? If so, is this the last opportunity for an attack?

For the first time since the Iranian nuclear threat emerged in the mid-1990s, at least some of Israel’s most powerful leaders believe that the response to all of these questions is yes.

At various points in our conversation, Barak underscored that if Israel or the rest of the world waits too long, the moment will arrive — sometime in the coming year, he says — beyond which it will no longer be possible to act. “It will not be possible to use any surgical means to bring about a significant delay,” he said. “Not for us, not for Europe and not for the United States. After that, the question will remain very important, but it will become purely theoretical and pass out of our hands — the statesmen and decision-makers — and into yours — the journalists and historians.”

Moshe Ya’alon, Israel’s vice prime minister and minister of strategic affairs, is the third leg in the triangle supporting a very aggressive stance toward Iran. When I spoke with him on the afternoon of Jan. 18, the same day that Barak stated publicly that any decision to strike pre-emptively was “very far off,” Ya’alon, while reiterating that an attack was the last option, took pains to emphasize Israel’s resolve. “Our policy is that in one way or another, Iran’s nuclear program must be stopped,” he said. “It is a matter of months before the Iranians will be able to attain military nuclear capability. Israel should not have to lead the struggle against Iran. It is up to the international community to confront the regime, but nevertheless Israel has to be ready to defend itself. And we are prepared to defend ourselves,” Ya’alon went on, “in any way and anywhere that we see fit.”

For years, Israeli and American intelligence agencies assumed that if Iran were to gain the ability to build a bomb, it would be a result of its relationship with Russia, which was building a nuclear reactor for Iran at a site called Bushehr and had assisted the Iranians in their missile-development program. Throughout the 1990s, Israel and the United States devoted vast resources to weakening the nuclear links between Russia and Iran and applied enormous diplomatic pressure on Russia to cut off the relationship. Ultimately, the Russians made it clear that they would do all in their power to slow down construction on the Iranian reactor and assured Israel that even if it was completed (which it later was), it wouldn’t be possible to produce the refined uranium or plutonium needed for nuclear weapons there.

But the Russians weren’t Iran’s only connection to nuclear power. Robert Einhorn, currently special adviser for nonproliferation and arms control at the U. S. State Department, told me in 2003: “Both countries invested huge efforts, overt and covert, in order to find out what exactly Russia was supplying to Iran and in attempts to prevent that supply. We were convinced that this was the main path taken by Iran to secure the Doomsday weapon. But only very belatedly did it emerge that if Iran one day achieved its goal, it will not be by the Russian path at all. It made its great advance toward nuclear weaponry on another path altogether — a secret one — that was concealed from our sight.”

That secret path was Iran’s clandestine relationship with the network of Abdul Qadeer Khan, the father of Pakistan’s atom bomb. Cooperation between American, British and Israeli intelligence services led to the discovery in 2002 of a uranium-enrichment facility built with Khan’s assistance at Natanz, 200 miles south of Tehran. When this information was verified, a great outcry erupted throughout Israel’s military and intelligence establishment, with some demanding that the site be bombed at once. Prime Minister Ariel Sharon did not authorize an attack. Instead, information about the site was leaked to a dissident Iranian group, the National Resistance Council, which announced that Iran was building a centrifuge installation at Natanz. This led to a visit to the site by a team of inspectors from the International Atomic Energy Agency, who were surprised to discover that Iran was well on its way to completing the nuclear fuel cycle — the series of processes for the enrichment of uranium that is a critical stage in producing a bomb.

Despite the discovery of the Natanz site and the international sanctions that followed, Israeli intelligence reported in early 2004 that Iran’s nuclear project was still progressing. Sharon assigned responsibility for putting an end to the program to Meir Dagan, then head of the Mossad. The two knew each other from the 1970s, when Sharon was the general in charge of the southern command of the Israel Defense Forces and Dagan was a young officer whom he put in charge of a top-secret unit whose purpose was the systematic assassination of Palestine Liberation Organization militiamen in the Gaza Strip. As Sharon put it at the time: “Dagan’s specialty is separating an Arab from his head.”

Sharon granted the Mossad virtually unlimited funds and powers to “stop the Iranian bomb.” As one recently retired senior Mossad officer told me: “There was no operation, there was no project that was not carried out because of a lack of funding.”

At a number of secret meetings with U.S. officials between 2004 and 2007, Dagan detailed a “five-front strategy” that involved political pressure, covert measures, counterproliferation, sanctions and regime change. In a secret cable sent to the U.S. in August 2007, he stressed that “the United States, Israel and like-minded countries must push on all five fronts in a simultaneous joint effort.” He went on to say: “Some are bearing fruit now. Others” — and here he emphasized efforts to encourage ethnic resistance in Iran — “will bear fruit in due time, especially if they are given more attention.”

From 2005 onward, various intelligence arms and the U.S. Treasury, working together with the Mossad, began a worldwide campaign to locate and sabotage the financial underpinnings of the Iranian nuclear project. The Mossad provided the Americans with information on Iranian firms that served as fronts for the country’s nuclear acquisitions and financial institutions that assisted in the financing of terrorist organizations, as well as a banking front established by Iran and Syria to handle all of these activities. The Americans subsequently tried to persuade several large corporations and European governments — especially France, Germany and Britain — to cease cooperating with Iranian financial institutions, and last month the Senate approved sanctions against Iran’s central bank.

In addition to these interventions, as well as to efforts to disrupt the supply of nuclear materials to Iran, since 2005 the Iranian nuclear project has been hit by a series of mishaps and disasters, for which the Iranians hold Western intelligence services — especially the Mossad — responsible. According to the Iranian media, two transformers blew up and 50 centrifuges were ruined during the first attempt to enrich uranium at Natanz in April 2006. A spokesman for the Iranian Atomic Energy Council stated that the raw materials had been “tampered with.” Between January 2006 and July 2007, three airplanes belonging to Iran’s Revolutionary Guards crashed under mysterious circumstances. Some reports said the planes had simply “stopped working.” The Iranians suspected the Mossad, as they did when they discovered that two lethal computer viruses had penetrated the computer system of the nuclear project and caused widespread damage, knocking out a large number of centrifuges.

In January 2007, several insulation units in the connecting fixtures of the centrifuges, which were purchased from a middleman on the black market in Eastern Europe, turned out to be flawed and unusable. Iran concluded that some of the merchants were actually straw companies that were set up to outfit the Iranian nuclear effort with faulty parts.

Of all the covert operations, the most controversial have been the assassinations of Iranian scientists working on the nuclear project. In January 2007, Dr. Ardeshir Husseinpour, a 44-year-old nuclear scientist working at the Isfahan uranium plant, died under mysterious circumstances. The official announcement of his death said he was asphyxiated “following a gas leak,” but Iranian intelligence is convinced that he was the victim of an Israeli assassination.

Massoud Ali Mohammadi, a particle physicist, was killed in January 2010, when a booby-trapped motorcycle parked nearby exploded as he was getting into his car. (Some contend that Mohammadi was not killed by the Mossad, but by Iranian agents because of his supposed support for the opposition leader Mir Hussein Moussavi.) Later that year, on Nov. 29, a manhunt took place in the streets of Tehran for two motorcyclists who had just blown up the cars of two senior figures in the Iranian nuclear project, Majid Shahriari and Fereydoun Abbasi-Davani. The motorcyclists attached limpet mines (also known as magnet bombs) to the cars and then sped away. Shahriari was killed by the blast in his Peugeot 405, but Abbassi-Davani and his wife managed to escape their car before it exploded. Following this assassination attempt, President Mahmoud Ahmadinejad appointed Abbassi-Davani vice president of Iran and head of the country’s atomic agency. Today he is heavily guarded wherever he goes, as is the scientific head of the nuclear project, Mohsin Fakhri-Zadeh, whose lectures at Tehran University were discontinued as a precautionary measure.

This past July, a motorcyclist ambushed Darioush Rezaei Nejad, a nuclear physicist and a researcher for Iran’s Atomic Energy Organization, as he sat in his car outside his house. The biker drew a pistol and shot the scientist dead through the car window.

Four months later, in November, a huge explosion occurred at a Revolutionary Guards base 30 miles west of Tehran. The cloud of smoke was visible from the city, where residents could feel the ground shake and hear their windows rattle, and satellite photos showed that almost the entire base was obliterated. Brig. Gen. Hassan Moghaddam, head of the Revolutionary Guards’ missile-development division, was killed, as were 16 of his personnel. Ayatollah Ali Khamenei, Iran’s spiritual leader, paid respect by coming to the funeral service for the general and visiting the widow at her home, where he called Moghaddam a martyr.

Just this month, on Jan. 11, two years after his colleague and friend Massoud Ali Mohammadi was killed, a deputy director at the Natanz uranium-enrichment facility named Mostafa Ahmadi-Roshan left his home and headed for a laboratory in downtown Tehran. A few months earlier, a photograph of him accompanying Ahmadinejad on a tour of nuclear installations appeared in newspapers across the globe. Two motorcyclists drove up to his car and attached a limpet mine that killed him on the spot.

Israelis cannot enter Iran, so Israel, Iranian officials believe, has devoted huge resources to recruiting Iranians who leave the country on business trips and turning them into agents. Some have been recruited under a false flag, meaning that the organization’s recruiters pose as other nationalities, so that the Iranian agents won’t know they are on the payroll of “the Zionist enemy,” as Israel is called in Iran. Also, as much as possible, the Mossad prefers to carry out its violent operations based on the blue-and-white principle, a reference to the colors of Israel’s national flag, which means that they are executed only by Israeli citizens who are regular Mossad operatives and not by assassins recruited in the target country. Operating in Iran, however, is impossible for the Mossad’s sabotage-and-assassination unit, known as Caesarea, so the assassins must come from elsewhere. Iranian intelligence believes that over the last several years, the Mossad has financed and armed two Iranian opposition groups, the Muhjahedin Khalq (MEK) and the Jundallah, and has set up a forward base in Kurdistan to mobilize the Kurdish minority in Iran, as well as other minorities, training some of them at a secret base near Tel Aviv.

Officially, Israel has never admitted any involvement in these assassinations, and after Secretary of State Hillary Clinton spoke out against the killing of Ahmadi-Roshan this month, President Shimon Peres said he had no knowledge of Israeli involvement. The Iranians vowed revenge after the murder, and on Jan. 13, as I spoke with Ehud Barak at his home in Tel Aviv, the country’s intelligence community was conducting an emergency operation to thwart a joint attack by Iran and Hezbollah against Israeli and Jewish targets in Bangkok. Local Thai forces, reportedly acting on information supplied by the Mossad, raided a Hezbollah hideout in Bangkok and later apprehended a member of the terror cell as he tried to flee the country. The prisoner reportedly confessed that he and his fellow cell members intended to blow up the Israeli Embassy and a synagogue.

Meir Dagan, while not taking credit for the assassinations, has praised the hits against Iranian scientists attributed to the Mossad, saying that beyond “the removal of important brains” from the project, the killings have brought about what is referred to in the Mossad as white defection — in other words, the Iranian scientists are so frightened that many have requested to be transferred to civilian projects. “There is no doubt,” a former top Mossad official told me over breakfast on Jan. 11, just a few hours after news of Ahmadi-Roshan’s assassination came from Tehran, “that being a scientist in a prestigious nuclear project that is generously financed by the state carries with it advantages like status, advancement, research budgets and fat salaries. On the other hand, when a scientist — one who is not a trained soldier or used to facing life-threatening situations, who has a wife and children — watches his colleagues being bumped off one after the other, he definitely begins to fear that the day will come when a man on a motorbike knocks on his car window.”

As we spoke, a man approached and, having recognized me as a journalist who reports on these issues, apologized before asking: “When is the war going to break out? When will the Iranians bomb us?” The Mossad official smiled as I tried to reassure the man that we wouldn’t be nuked tomorrow. Similar scenes occur almost every day — Israelis watch the news, have heard that bomb shelters are being prepared, know that Israel test-fired a missile into the sea two months ago — and a kind of panic has begun to overtake Israeli society, anxiety that missiles will start raining down soon.

Dagan believes that his five-fronts strategy has succeeded in significantly delaying Iran’s progress toward developing nuclear weapons; specifically “the use of all the weapons together,” he told me and a small group of Israeli journalists early last year. “In the mind of the Iranian citizen, a link has been created between his economic difficulties and the nuclear project. Today in Iran, there is a profound internal debate about this matter, which has divided the Iranian leadership.” He beamed when he added, “It pleases me that the timeline of the project has been pushed forward several times since 2003 because of these mysterious disruptions.”

Barak and Netanyahu are less convinced of the Mossad’s long-term success. From the beginning of their terms (Barak as defense minister in June 2007, Netanyahu as prime minister in March 2009), they have held the opinion that Israel must have a military option ready in case covert efforts fail. Barak ordered extensive military preparations for an attack on Iran that continue to this day and have become more frequent in recent months. He was not alone in fearing that the Mossad’s covert operations, combined with sanctions, would not be sufficient. The I.D.F. and military intelligence have also experienced waning enthusiasm. Three very senior military intelligence officers, one who is still serving and two who retired recently, told me that with all due respect for Dagan’s success in slowing down the Iranian nuclear project, Iran was still making progress. One recalled Israel’s operations against Iraq’s nuclear program in the late 1970s, when the Mossad eliminated some of the scientists working on the project and intimidated others. On the night of April 6, 1979, a team of Mossad operatives entered the French port town La Seyne-sur-Mer and blew up a shipment necessary for the cooling system of the Iraqi reactor’s core that was being manufactured in France. The French police found no trace of the perpetrators. An unknown organization for the defense of the environment claimed responsibility.

The attack was successful, but a year later the damage was repaired and further sabotage efforts were thwarted. The project advanced until late in 1980, when it was discovered that a shipment of fuel rods containing enriched uranium had been sent from France to Baghdad, and they were about to be fed into the reactor’s core. Israel determined that it had no other option but to launch Operation Opera, a surprise airstrike in June 1981 on the Tammuz-Osirak reactor just outside Baghdad.

Similarly, Dagan’s critics say, the Iranians have managed to overcome most setbacks and to replace the slain scientists. According to latest intelligence, Iran now has some 10,000 functioning centrifuges, and they have streamlined the enrichment process. Iran today has five tons of low-grade fissile material, enough, when converted to high-grade material, to make about five to six bombs; it also has about 175 pounds of medium-grade material, of which it would need about 500 pounds to make a bomb. It is believed that Iran’s nuclear scientists estimate that it will take them nine months, from the moment they are given the order, to assemble their first explosive device and another six months to be able to reduce it to the dimensions of a payload for their Shahab-3 missiles, which are capable of reaching Israel. They are holding the fissile material at sites across the country, most notably at the Fordo facility, near the holy city Qom, in a bunker that Israeli intelligence estimates is 220 feet deep, beyond the reach of even the most advanced bunker-busting bombs possessed by the United States.

Barak serves as the senior Israeli representative in the complex dialogue with the United States on this topic. He disagrees with the parallels that some Israeli politicians, mainly his boss, Netanyahu, draw between Ahmadinejad and Adolf Hitler, and espouses far more moderate views. “I accept that Iran has other reasons for developing nuclear bombs, apart from its desire to destroy Israel, but we cannot ignore the risk,” he told me earlier this month. “An Iranian bomb would ensure the survival of the current regime, which otherwise would not make it to its 40th anniversary in light of the admiration that the young generation in Iran has displayed for the West. With a bomb, it would be very hard to budge the administration.” Barak went on: “The moment Iran goes nuclear, other countries in the region will feel compelled to do the same. The Saudi Arabians have told the Americans as much, and one can think of both Turkey and Egypt in this context, not to mention the danger that weapons-grade materials will leak out to terror groups.

“From our point of view,” Barak said, “a nuclear state offers an entirely different kind of protection to its proxies. Imagine if we enter another military confrontation with Hezbollah, which has over 50,000 rockets that threaten the whole area of Israel, including several thousand that can reach Tel Aviv. A nuclear Iran announces that an attack on Hezbollah is tantamount to an attack on Iran. We would not necessarily give up on it, but it would definitely restrict our range of operations.”

At that point Barak leaned forward and said with the utmost solemnity: “And if a nuclear Iran covets and occupies some gulf state, who will liberate it? The bottom line is that we must deal with the problem now.”

He warned that no more than one year remains to stop Iran from obtaining nuclear weaponry. This is because it is close to entering its “immunity zone” — a term coined by Barak that refers to the point when Iran’s accumulated know-how, raw materials, experience and equipment (as well as the distribution of materials among its underground facilities) — will be such that an attack could not derail the nuclear project. Israel estimates that Iran’s nuclear program is about nine months away from being able to withstand an Israeli attack; America, with its superior firepower, has a time frame of 15 months. In either case, they are presented with a very narrow window of opportunity. One very senior Israeli security source told me: “The Americans tell us there is time, and we tell them that they only have about six to nine months more than we do and that therefore the sanctions have to be brought to a culmination now, in order to exhaust that track.”

Many European analysts and some intelligence agencies have in the past responded to Israel’s warnings with skepticism, if not outright suspicion. Some have argued that Israel has intentionally exaggerated its assessments to create an atmosphere of fear that would drag Europe into its extensive economic campaign against Iran, a skepticism bolstered by the C.I.A.’s incorrect assessment about Iraqi W.M.D. before to the Iraq war.

Israel’s discourse with the United States on the subject of Iran’s nuclear project is more significant, and more fraught, than it is with Europe. The U.S. has made efforts to stiffen sanctions against Iran and to mobilize countries like Russia and China to apply sanctions in exchange for substantial American concessions. But beneath the surface of this cooperation, there are signs of mutual suspicion. As one senior American official wrote to the State Department and the Pentagon in November 2009, after an Israeli intelligence projection that Iran would have a complete nuclear arsenal by 2012: “It is unclear if the Israelis firmly believe this or are using worst-case estimates to raise greater urgency from the United States.”

For their part, the Israelis suspect that the Obama administration has abandoned any aggressive strategy that would ensure the prevention of a nuclear Iran and is merely playing a game of words to appease them. The Israelis find evidence of this in the shift in language used by the administration, from “threshold prevention” — meaning American resolve to stop Iran from having a nuclear-energy program that could allow for the ability to create weapons — to “weapons prevention,” which means the conditions can exist, but there is an American commitment to stop Iran from assembling an actual bomb.

“I fail to grasp the Americans’ logic,” a senior Israeli intelligence source told me. “If someone says we’ll stop them from getting there by praying for more glitches in the centrifuges, I understand. If someone says we must attack soon to stop them, I get it. But if someone says we’ll stop them after they are already there, that I do not understand.”

Over the past year, Western intelligence agencies, in particular the C.I.A., have moved closer to Israel’s assessments of the Iranian nuclear project. Defense Secretary Leon Panetta expressed this explicitly when he said that Iran would be able to reach nuclear-weapons capabilities within a year. The International Atomic Energy Agency published a scathing report stating that Iran was in breach of the Nuclear Nonproliferation Treaty and was possibly trying to develop nuclear weapons. Emboldened by this newfound accord, Israel’s leaders have adopted a harsher tone against Iran. Ya’alon, the deputy prime minister, told me in October: “We have had some arguments with the U.S. administration over the past two years, but on the Iranian issue we have managed to close the gaps to a certain extent. The president’s statements at his last meeting with the prime minister — that ‘we are committed to prevent ’ and ‘all the options are on the table’ — are highly important. They began with the sanctions too late, but they have moved from a policy of engagement to a much more active (sanctions) policy against Iran. All of these are positive developments.” On the other hand, Ya’alon sighed as he admitted: “The main arguments are ahead of us. This is clear.”

Now that the facts have been largely agreed upon, the arguments Ya’alon anticipates are those that will stem from the question of how to act — and what will happen if Israel decides that the moment for action has arrived. The most delicate issue between the two countries is what America is signaling to Israel and whether Israel should inform America in advance of a decision to attack.

Matthew Kroenig is the Stanton Nuclear Security Fellow at the Council on Foreign Relations and worked as a special adviser in the Pentagon from July 2010 to July 2011. One of his tasks was defense policy and strategy on Iran. When I spoke with Kroenig last week, he said: “My understanding is that the United States has asked Israel not to attack Iran and to provide Washington with notice if it intends to strike. Israel responded negatively to both requests. It refused to guarantee that it will not attack or to provide prior notice if it does.” Kroenig went on, “My hunch is that Israel would choose to give warning of an hour or two, just enough to maintain good relations between the countries but not quite enough to allow Washington to prevent the attack.” Kroenig said Israel was correct in its timeline of Iran’s nuclear development and that the next year will be critical. “The future can evolve in three ways,” he said. “Iran and the international community could agree to a negotiated settlement; Israel and the United States could acquiesce to a nuclear-armed Iran; or Israel or the United States could attack. Nobody wants to go in the direction of a military strike,” he added, “but unfortunately this is the most likely scenario. The more interesting question is not whether it happens but how. The United States should treat this option more seriously and begin gathering international support and building the case for the use of force under international law.”

In June 2007, I met with a former director of the Mossad, Meir Amit, who handed me a document stamped, “Top secret, for your eyes only.” Amit wanted to demonstrate the complexity of the relations between the United States and Israel, especially when it comes to Israeli military operations in the Middle East that could significantly impact American interests in the region.

Almost 45 years ago, on May 25, 1967, in the midst of the international crisis that precipitated the Six-Day War, Amit, then head of the Mossad, summoned John Hadden, the C.I.A. chief in Tel Aviv, to an urgent meeting at his home. The meeting took place against the background of the mounting tensions in the Middle East, the concentration of a massive Egyptian force in the Sinai Peninsula, the closing of the Straits of Tiran to Israeli shipping and the threats by President Gamal Abdel Nasser to destroy the State of Israel.

In what he later described as “the most difficult meeting I have ever had with a representative of a foreign intelligence service,” Amit laid out Israel’s arguments for attacking Egypt. The conversation between them, which was transcribed in the document Amit passed on to me, went as follows:

Amit: “We are approaching a turning point that is more important for you than it is for us. After all, you people know everything. We are in a grave situation, and I believe we have reached it, because we have not acted yet. . . . Personally, I am sorry that we did not react immediately. It is possible that we may have broken some rules if we had, but the outcome would have been to your benefit. I was in favor of acting. We should have struck before the build-up.”

Hadden: “That would have brought Russia and the United States against you.”

Amit: “You are wrong. . . . We have now reached a new stage, after the expulsion of the U.N. inspectors. You should know that it’s your problem, not ours.”

Hadden: “Help us by giving us a good reason to come in on your side. Get them to fire at something, a ship, for example.”

Amit: “That is not the point.”

Hadden: “If you attack, the United States will land forces to help the attacked state protect itself.”

Amit: “I can’t believe what I am hearing.”

Hadden: “Do not surprise us.”

Amit: “Surprise is one of the secrets of success.”

Hadden: “I don’t know what the significance of American aid is for you.”

Amit: “It isn’t aid for us, it is for yourselves.”

That ill-tempered meeting, and Hadden’s threats, encouraged the Israeli security cabinet to ban the military from carrying out an immediate assault against the Egyptian troops in the Sinai, although they were perceived as a grave threat to the existence of Israel. Amit did not accept Hadden’s response as final, however, and flew to the United States to meet with Defense Secretary Robert McNamara. Upon his return, he reported to the Israeli cabinet that when he told McNamara that Israel could not reconcile itself to Egypt’s military actions, the secretary replied, “I read you very clearly.” When Amit then asked McNamara if he should remain in Washington for another week, to see how matters developed, McNamara responded, “Young man, go home, that is where you are needed now.”

From this exchange, Amit concluded that the United States was giving Israel “a flickering green light” to attack Egypt. He told the cabinet that if the Americans were given one more week to exhaust their diplomatic efforts, “they will hesitate to act against us.” The next day, the cabinet decided to begin the Six-Day War, which changed the course of Middle Eastern history.

Amit handed me the minutes of that conversation from the same armchair that he sat in during his meeting with Hadden. It is striking how that dialogue anticipated the one now under way between Israel and the United States. Substitute “Tehran” for “Cairo” and “Strait of Hormuz” for “Straits of Tiran,” and it could have taken place this past week. Since 1967, the unspoken understanding that America should agree, at least tacitly, to Israeli military actions has been at the center of relations between the two countries.

During my lengthy conversation with Barak, I pulled out the transcript of the Amit-Hadden meeting. Amit was his commander when Barak was a young officer, in a unit that carried out commando raids deep inside enemy territory. Barak, a history buff, smiled at the comparison, and then he completely rejected it. “Relations with the United States are far closer today,” he said. “There are no threats, no recriminations, only cooperation and mutual respect for each other’s sovereignty.”

In our conversation on Jan. 18, Ya’alon, the deputy prime minister, was sharp in his criticism of the international community’s stance on Iran. “These are critical hours on the question of which way the international community will take the policy,” he said. “The West must stand united and resolute, and what is happening so far is not enough. The Iranian regime must be placed under pressure and isolated. Sanctions that bite must be imposed against it, something that has not happened as yet, and a credible military option should be on the table as a last resort. In order to avoid it, the sanctions must be stepped up.” It is, of course, important for Ya’alon to argue that this is not just an Israeli-Iranian dispute, but a threat to America’s well-being. “The Iranian regime will be several times more dangerous if it has a nuclear device in its hands,” he went on. “One that it could bring into the United States. It is not for nothing that it is establishing bases for itself in Latin America and creating links with drug dealers on the U.S.-Mexican border. This is happening in order to smuggle ordnance into the United States for the carrying out of terror attacks. Imagine this regime getting nuclear weapons to the U.S.-Mexico border and managing to smuggle it into Texas, for example. This is not a far-fetched scenario.”

Ehud Barak dislikes this kind of criticism of the United States, and in a rather testy tone in a phone conversation with me on Jan. 18 said: “Our discourse with the United States is based on listening and mutual respect, together with an understanding that it is our primary ally. The U.S. is what helps us to preserve the military advantage of Israel, more than ever before. This administration contributes to the security of Israel in an extraordinary way and does a lot to prevent a nuclear Iran. We’re not in confrontation with America. We’re not in agreement on every detail, we can have differences — and not unimportant ones — but we should not talk as if we are speaking about a hostile entity.”

Over the last four years, since Barak was appointed minister of defense, the Israeli military has prepared in unprecedented ways for a strike against Iran. It has also grappled with questions of how it will manage the repercussions of such an attack. Much of the effort is dedicated to strengthening the country’s civil defenses — bomb shelters, air-raid sirens and the like — areas in which serious defects were discovered during the war against Hezbollah in Lebanon in the summer of 2006. Civilian disaster exercises are being held intermittently, and gas masks have been distributed to the population.

On the operational level, any attack would be extremely complex. Iran learned the lessons of Iraq, and has dispersed its nuclear installations throughout its vast territory. There is no way of knowing for certain if the Iranians have managed to conceal any key facilities from Israeli intelligence. Israel has limited air power and no aircraft carriers. If it attacked Iran, because of the 1,000 or so miles between its bases and its potential targets, Israeli planes would have to refuel in the air at least once (and more than once if faced with aerial engagements). The bombardment would require pinpoint precision in order to spend the shortest amount of time over the targets, which are heavily defended by antiaircraft-missile batteries.

In the end, a successful attack would not eliminate the knowledge possessed by the project’s scientists, and it is possible that Iran, with its highly developed technological infrastructure, would be able to rebuild the damaged or wrecked sites. What is more, unlike Syria, which did not respond after the destruction of its reactor in 2007, Iran has openly declared that it would strike back ferociously if attacked. Iran has hundreds of Shahab missiles armed with warheads that can reach Israel, and it could harness Hezbollah to strike at Israeli communities with its 50,000 rockets, some of which can hit Tel Aviv. (Hamas in Gaza, which is also supported by Iran, might also fire a considerable number of rockets on Israeli cities.) According to Israeli intelligence, Iran and Hezbollah have also planted roughly 40 terrorist sleeper cells across the globe, ready to hit Israeli and Jewish targets if Iran deems it necessary to retaliate. And if Israel responded to a Hezbollah bombardment against Lebanese targets, Syria may feel compelled to begin operations against Israel, leading to a full-scale war. On top of all this, Tehran has already threatened to close off the Persian Gulf to shipping, which would generate a devastating ripple through the world economy as a consequence of the rise in the price of oil.

The proponents of an attack argue that the problems delineated above, including missiles from Iran and Lebanon and terror attacks abroad, are ones Israel will have to deal with regardless of whether it attacks Iran now — and if Iran goes nuclear, dealing with these problems will become far more difficult.

The Israeli Air Force is where most of the preparations are taking place. It maintains planes with the long-range capacity required to deliver ordnance to targets in Iran, as well as unmanned aircraft capable of carrying bombs to those targets and remaining airborne for up to 48 hours. Israel believes that these platforms have the capacity to cause enough damage to set the Iranian nuclear project back by three to five years.

In January 2010, the Mossad sent a hit team to Dubai to liquidate the high-ranking Hamas official Mahmoud al-Mabhouh, who was coordinating the smuggling of rockets from Iran to Gaza. The assassination was carried out successfully, but almost the entire operation and all its team members were recorded on closed-circuit surveillance TV cameras. The operation caused a diplomatic uproar and was a major embarrassment for the Mossad. In the aftermath, Netanyahu decided not to extend Dagan’s already exceptionally long term, informing him that he would be replaced in January 2011. That decision was not well received by Dagan, and three days before he was due to leave his post, I and several other Israeli journalists were surprised to receive invitations to a meeting with him at Mossad headquarters.

We were told to congregate in the parking lot of a movie-theater complex north of Tel Aviv, where we were warned by Mossad security personnel, “Do not bring computers, recording devices, cellphones. You will be carefully searched, and we want to avoid unpleasantness. Leave everything in your cars and enter our vehicles carrying only paper and pens.” We were then loaded into cars with opaque windows and escorted by black Jeeps to a site that we knew was not marked on any map. The cars went through a series of security checks, requiring our escorts to explain who we were and show paperwork at each roadblock.

This was the first time in the history of the Mossad that a group of journalists was invited to meet the director of the organization at one of the country’s most secret sites. After the search was performed and we were seated, the outgoing chief entered the room. Dagan, who was wounded twice in combat, once seriously, during the Six-Day War, started by saying: “There are advantages to being wounded in the back. You have a doctor’s certificate that you have a backbone.” He then went into a discourse about Iran and sharply criticized the heads of government for even contemplating “the foolish idea” of attacking it.

“The use of state violence has intolerable costs,” he said. “The working assumption that it is possible to totally halt the Iranian nuclear project by means of a military attack is incorrect. There is no such military capability. It is possible to cause a delay, but even that would only be for a limited period of time.”

He warned that attacking Iran would start an unwanted war with Hezbollah and Hamas: “I am not convinced that Syria will not be drawn into the war. While the Syrians won’t charge at us in tanks, we will see a massive offensive of missiles against our home front. Civilians will be on the front lines. What is Israel’s defensive capability against such an offensive? I know of no solution that we have for this problem.”

Asked if he had said these things to Israel’s decision-makers, Dagan replied: “I have expressed my opinion to them with the same emphasis as I have here now. Sometimes I raised my voice, because I lose my temper easily and am overcome with zeal when I speak.”

In later conversations Dagan criticized Netanyahu and Barak, and in a lecture at Tel Aviv University he observed, “The fact that someone has been elected doesn’t mean that he is smart.”

In the audience at that lecture was Rafi Eitan, 85, one of the Mossad’s most seasoned and well-known operatives. Eitan agreed with Dagan that Israel lacked the capabilities to attack Iran. When I spoke with him in October, Eitan said: “As early as 2006 (when Eitan was a senior cabinet minister), I told the cabinet that Israel couldn’t afford to attack Iran. First of all, because the home front is not ready. I told anyone who wanted and still wants to attack, they should just think about two missiles a day, no more than that, falling on Tel Aviv. And what will you do then? Beyond that, our attack won’t cause them significant damage. I was told during one of the discussions that it would delay them for three years, and I replied, ‘Not even three months.’ After all, they have scattered their facilities all over the country and under the ground. ‘What harm can you do to them?’ I asked. ‘You’ll manage to hit the entrances, and they’ll have them rebuilt in three months.’ ”

Asked if it was possible to stop a determined Iran from becoming a nuclear power, Eitan replied: “No. In the end they’ll get their bomb. The way to fight it is by changing the regime there. This is where we have really failed. We should encourage the opposition groups who turn to us over and over to ask for our help, and instead, we send them away empty-handed.”

Israeli law stipulates that only the 14 members of the security cabinet have the authority to make decisions on whether to go to war. The cabinet has not yet been asked to vote, but the ministers might, under pressure from Netanyahu and Barak, answer these crucial questions about Iran in the affirmative: that these coming months are indeed the last opportunity to attack before Iran enters the “immunity zone”; that the broad international agreement on Iran’s intentions and the failure of sanctions to stop the project have created sufficient legitimacy for an attack; and that Israel does indeed possess the capabilities to cause significant damage to the Iranian project.

In recent weeks, Israelis have obsessively questioned whether Netanyahu and Barak are really planning a strike or if they are just putting up a front to pressure Europe and the U.S. to impose tougher sanctions. I believe that both of these things are true, but as a senior intelligence officer who often participates in meetings with Israel’s top leadership told me, the only individuals who really know their intentions are, of course, Netanyahu and Barak, and recent statements that no decision is imminent must surely be taken into account.

After speaking with many senior Israeli leaders and chiefs of the military and the intelligence, I have come to believe that Israel will indeed strike Iran in 2012. Perhaps in the small and ever-diminishing window that is left, the United States will choose to intervene after all, but here, from the Israeli perspective, there is not much hope for that. Instead there is that peculiar Israeli mixture of fear — rooted in the sense that Israel is dependent on the tacit support of other nations to survive — and tenacity, the fierce conviction, right or wrong, that only the Israelis can ultimately defend themselves.