In the first eight days of Israel's battle against Hamas, the conflict was fought from the air, with Israeli fighter jets striking from the skies on targets in Gaza, and with Hamas firing unguided rockets with the hope they would land on Israelis living in cities as far as 25 miles away.

On Saturday, Israel altered that strategy, bringing the war to Hamas's doorstep with a ground invasion of the Gaza Strip. In so doing, Israeli leaders run the risk of repeating their disastrous experience in the 2006 Lebanon war, when they suffered high casualties in ground combat with Hezbollah, and they may face political fallout in elections less than two months away.

For Hamas, the Israeli attacks have taken a heavy toll in death and destruction, wiping out not only security and police buildings but also homes, mosques and a university that are all part of its network in the strip. The Hamas goal, analysts say, is not so much to win militarily but rather to exact a psychological victory, in the same way Hezbollah bolstered its legitimacy both inside Lebanon and in the Arab world after its war.

Many believe that the ground invasion could give Hamas, with superior knowledge of Gaza's terrain, an advantage over Israel's troops. "If you enter Gaza by land, a dark fate will await you," top Hamas political leader Khaled Mashal threatened Israel in a televised interview Friday from exile in Damascus, Syria.

Over the past four years, Israel has sought to block the Palestinians from using some of their most devastating, close-range tactics: suicide bombings and small arms in guerrilla-style strikes. Those kinds of attacks were favored by Palestinians during the second intifada, or uprising, earlier this decade, and were effective in killing Israelis. But they are much more difficult to pull off today.

Israel has built fences and walls around the Gaza Strip and the bulk of the West Bank. It has dramatically curtailed movement in both places, setting up internal checkpoints in the West Bank and preventing the vast majority of Gaza's 1.5 million people from leaving the narrow coastal territory. In 2005, Israel pulled its troops and its settlers from Gaza, after which Hamas and its allies turned almost exclusively to rockets -- many of them made in local metalwork shops -- to strike at Israel.

At the same time, Israel has significantly upgraded its air capabilities, adding armed, unmanned aerial vehicles and advanced, precision-guided bombs and missiles.

The result has been a dramatic change in the casualty ratios as the battle moved from the ground to the sky. In 2002, at the height of the second intifada, more than 1,000 Palestinians were killed, compared with about 400 Israelis. In the past eight days of war, more than 460 Palestinians were killed, and four Israelis died by rocket fire. There were no Israeli military casualties in the air campaign.

For Yoav Amit, a school administrative manager in Beersheba, such statistics provided little comfort. On Thursday, he inspected a huge hole in a ninth-grade classroom, where a rocket had torn into the ceiling. "We can't depend only on airstrikes," he said. "We have no choice but to send ground troops into Gaza."

Still, he said, he worried about Israel's soldiers. "It didn't succeed in Lebanon," said Amit, who served in the Israeli air force during the 1973 Mideast war. "The same thing might happen in Gaza."
Echoes of Hezbollah War

In the summer of 2006, Hezbollah, the Iranian-backed Shiite militia, fought Israel in 33 days of war. The Israeli military's goal was to end Hezbollah rocket fire into northern Israel and to bring back two soldiers who had been seized in a cross-border raid. But after weeks of airstrikes, the rocket fire continued, with Hezbollah firing thousands of Katyushas over the course of the war.

Israel launched a major ground invasion in the final days of the conflict. In all, nearly 120 Israeli soldiers were killed, along with 43 Israeli civilians and more than 1,100 Lebanese. In the aftermath, much of the Muslim world lauded Hezbollah as victorious; today, the movement partially controls the government.

In Israel, meanwhile, reaction to the Lebanon war was decidedly negative. The defense minister and the military's chief of staff ultimately lost their jobs; Prime Minister Ehud Olmert only narrowly avoided losing his office amid mass protests calling for his ouster. Today, international monitors keep the peace in southern Lebanon, and Hezbollah has stopped firing rockets into northern Israel. But the militia is widely believed to have rebuilt its military capabilities, possessing an even larger armory of rockets.

"The dilemmas are the same as Lebanon, except much worse with Gaza," said Gershom Gorenberg, an Israeli author who has written extensively about Israeli-Palestinian issues. "You're dealing with a nonstate actor who's radical. Nobody wants to repeat an occupation [in Gaza]. What makes things worse in Gaza is that no international force is going to want to come in and control the situation."

In Lebanon, the Israeli military believed that the only way to stop a popular movement using guerrilla tactics was to cross into their territory, clear it and take it over, said Shlomo Brom, a retired Israeli brigadier general. "I don't think we have those illusions now," he said. "We don't want to occupy the Gaza Strip."

In Lebanon, Israel's tactics were piecemeal and not overpowering, he added. In Gaza, it has been anything but that. "If you decided to take a military step, it should be a crushing one with massive force, and that was the air campaign," said Brom, predicting that the same nature of force will be used in the land campaign.

Israeli jets have pounded Hamas government buildings and suspected weapons facilities and training camps. They have also targeted the buildings and institutions -- mosques, a police training academy, colleges -- that Israel believes formed the backbone of Hamas's social and political programs, from which they derive power and new recruits.

To Israelis, the goal of going into Gaza on the ground would be to try to seize the psychological advantage over Hamas and force the group to halt the rocket fire.

"The goal of the operation is to restore deterrence to our southern border. And deterrence is a matter of perception," said Isaac Ben-Israel, a member of the Israeli parliament from the ruling Kadima party and a retired Israeli major general. "If we hit them hard enough, they might come to the conclusion that they shouldn't fire any more rockets. But that won't be achieved without a ground campaign."

Gen. Eitan Ben Eliyahu, former chief of the Israeli air force, said that once Israel runs out of targets to strike by air, a ground incursion is needed for three reasons: "to suppress the sites where they launch the rockets into our home front; to fight them and kill more and more terrorists; and third, to tighten the ring of pressure around the Hamas leadership, which helps you conduct your negotiations in the diplomatic field."

Ben-Israel acknowledged that a ground campaign carries risks. Flying high over Gaza with sophisticated missile-evasion technology at their fingertips, Israeli airmen are largely out of range of Hamas attacks; not so for the soldiers, who could find themselves fighting Hamas block to block through Gaza's densely packed cities.

"The technological advantage we have is more demonstrable in the air. Not so much on the ground," Ben-Israel said.

Some analysts said that a ground invasion was not necessary if the goal is to destroy Hamas's military capabilities. Israeli airstrikes have destroyed tunnels used to funnel weapons and supplies, and demolished the houses and offices of Hamas leaders, killing two senior officials.

"The war in Kosovo was won from the air," said Hirsh Goodman, a senior fellow at the Institute for National Security Studies at Tel Aviv University, and a journalist for many years. "Here, Hamas has got nowhere to go and nowhere to get supplies from. They're firing whatever they can, but they've shot their wad.

"By punching into Gaza in several places, you can cut it into parcels, make it impossible for Hamas to govern, and exert a lot of pressure that way," he added. "But there will be burning tanks and human sacrifices, and it's not going to be pretty."

Others were more blunt. "What's wrong with the air war? Do you prefer ground forces moving into the Gaza Strip and finding themselves encircled by one and half million Palestinians?" said Shlomo Gazit, a retired major general who was in charge of the Israeli-occupied West Bank and Gaza Strip from 1967 to 1974. "It's a guaranteed catastrophe for the people in Gaza and for us."
Hamas's Political Gain

Over the past eight years, Hamas has steadily built up the size and sophistication of its rocket arsenal. The group, along with allies such as Islamic Jihad, has fired nearly 7,000 rockets into Israel since Israeli troops pulled out of Gaza in 2005.

Most, however, have been relatively ineffective rockets known as Qassams. Since 2005, 13 Israeli civilians have been killed by rocket fire from the strip.

Many of the rockets fired over the past week have had a greater range than the Qassams and have been similar in style to the Katyusha rockets employed by Hezbollah in 2006. Israeli military officials contend that Iran was the source of these rockets and that they were smuggled in by sea or by tunnel at the Egyptian border during the six-month cease-fire that ended in mid-December.

But Hamas's capacities are still limited. "Hamas has no real tools to fight the Israelis. They're not Hezbollah," said Nabil Kukali, director of the Bethlehem-based Palestinian Center for Public Opinion.

Still, there is a political benefit for Hamas in continuing to fire, even if the rocket attacks are no match for Israel's vastly superior military technology.

With Hamas's political rival, Fatah, committed to negotiating with Israel rather than fighting it, Hamas has a virtual monopoly on armed Palestinian resistance. That status has the potential to add to the movement's popularity among Palestinians, and in the broader Arab world.

"In 2006, Israel was helpless in the face of rocket fire from Hezbollah. And Hamas has learned from Hezbollah's experience," said Ziad Abu Zayyad, a former Palestinian negotiator who publishes a journal on the conflict.

Abu Zayyad said Hamas's reputation may grow even further if it can draw Israel into a ground war and then exact a heavy toll through a protracted insurgency.

"Israel may know how to enter Gaza," Abu Zayyad said. "But I'm not sure they know how to get out."