JERUSALEM — Gen. Martin E. Dempsey, chairman of the Joint Chiefs of Staff, arrived in Israel on Thursday for a 24-hour visit with the country’s top leaders that is expected to focus on Iran’s nuclear program as well as the challenges posed by the past year’s regional upheavals and the American military exit from Iraq.

This is General Dempsey’s first visit to Israel since taking over as chairman in October, and he is to meet with Prime Minister Benjamin Netanyahu, President Shimon Peres, Defense Minister Ehud Barak and Lt. Gen. Benny Gantz, the military chief of staff. He will also visit Yad Vashem, the Holocaust memorial and museum. He arrives after a visit to Europe.

Israel and the United States both say that Iran is pursuing the building of nuclear weapons — an assertion denied by Tehran — but they have had differing views on how aggressive the pursuit has been and what should be done about it. Both countries say that if Iran achieved that goal it would pose enormous dangers to them, their allies and Iran’s neighbors and would set off a lethal nuclear arms race in a highly unstable region. Both say they are committed to preventing Iran from building nuclear weapons.

Israel has frequently raised the possibility of military action against Iran if other means fail to halt Tehran’s nuclear work, but it would prefer to have the United States take the lead.

The Americans, while agreeing that force could be a last resort, have said that the first steps must be diplomacy and sanctions. Israel has publicly agreed that if sanctions are sufficiently tough, they could have the desired effect because the Iranian economy is shaky and the government may well respond to such measures.

Mr. Netanyahu said last week that he noticed that Iran was wobbling under the current sanctions and then said later that even stronger ones were needed. And Mr. Barak said on Wednesday that any Israeli decision on military action against Iran was “far off.” There has been widespread speculation that American officials like General Dempsey are sent here to get to the bottom of Israeli intentions or to persuade the Israelis not to take what the United States regards as rash action. Mr. Barak denied that such an effort was the point of this trip, however, saying, “The chairman of the Joint Chiefs of Staff is not coming with a view to putting pressure on the state of Israel.”

This week, the Israelis announced that a huge joint military exercise with American troops planned for the spring had been postponed to the second half of the year, apparently to reduce regional tensions.

Israeli officials say that while the two countries view the intelligence on Iranian nuclear endeavors in the same way, Israel feels more vulnerable about them. It is especially worried about Iran’s recent decision to move some uranium enrichment to a site deep underground, making any attack less likely to succeed. Officials here speak of their concern about Iranian “zones of immunity” that will make stopping the construction of weapons much harder.

But there is a strong strain of thought here and more so abroad that says an Israeli attack on Iran could be catastrophic, prompting a military counterattack as well as further radicalizing the region and isolating Israel.

Apart from sanctions and plans for military action, it appears that Israel, the United States and other Western countries have disrupted Iran’s nuclear program through sabotage: the sale of faulty parts and the introduction of computer worms and malfunctions. Five Iranian nuclear scientists have also been killed under mysterious circumstances. Iran has vowed to avenge their deaths.

For President Obama, tensions over Iran could make his re-election this year more complicated, especially if oil and gasoline prices rise as a result, causing hardship for American consumers. But his Republican opponents are much more hawkish on Iran and Israel’s other enemies so he faces pressure from both directions.

Iran’s intentions seem only more alarming to Israeli strategists as country after country in the region has undergone radical change and the power of political Islam grows.