The top U.S. general, visiting Israel at a delicate and dangerous moment in the global standoff with Tehran, is expected to press for restraint amid fears that the Jewish state is nearing a decision to attack Iran's nuclear program.
Thursday's arrival of Army Gen. Martin Dempsey, just four months after he took office as chairman of the Joint Chiefs of Staff, underscores Washington's concern about a possible Israeli military strike.
It also spotlights key questions at the center of the global maneuvering to prevent an Iranian bomb:
_ How effective are the current economic sanctions in pressuring Iran's leadership? Israel wants a far tougher regime, while the Americans seem confident the current path will suffice.
_ Could aerial bombardment or missile strikes, the expected Israeli military toolkit, damage nuclear installations deep underground enough to be worth a counterstrike from Iran? Some think Israel is mainly saber-rattling to scare governments into tougher sanctions.
_ Might covert activity suffice? Iranian scientists and military officials have been killed, computer viruses unleashed, a missile base blown up. Finger-pointing and denials abound; evidence about who's behind it all does not.
_ Could Israel really surprise Washington, its main ally and protector, with a military move that could affect America itself, in an election year to boot? Israeli officials have not pledged to give advance warning.
In the background, rarely openly discussed, is the somewhat prickly relationship between the Obama administration and the rightist government in Israel. The antipathy, born largely of disagreements on the Palestinian front, may not be helping navigate a situation as delicate as Iran.
But the main thing for Israel is the acute sense that a Rubicon is about to be crossed _ that a nuclear-armed Iran, whose President Mahmoud Ahmadinejad calls for Israel's destruction, is a direct existential threat.
Most of the West does agree with Israel that Iran, despite denials, is developing nuclear weapons technology. But the United States is clearly concerned that a military attack could backfire, fragmenting international opposition to Iran and sending oil prices skyrocketing.
Beginning Friday, Dempsey is set to meet with Prime Minister Benjamin Netanyahu and much of Israel's political and military leadership. Israeli officials involved in the preparations for the meetings said they expected Dempsey to urge restraint as the U.S. tries to rally additional global pressure on Iran. They spoke on condition of anonymity because of the sensitivity of the visit.
In a joint statement, the U.S. and Israel said the visit would focus on "cooperation between the two militaries, as well as mutual security challenges."
Israeli Cabinet Minister Dan Meridor, whose responsibilities include monitoring the Iranian nuclear program, said there was broad agreement with the Americans and the West on the need to stop the Iranians. "If the sanctions work, then all the other options will remain strictly theoretical," he said.
An air raid on Iran would require flying over potentially hostile Arab airspace and could well trigger a response from Iran, which possesses an arsenal of missiles capable of striking Israel. The Iranians could also encourage their proxies, Hezbollah in Lebanon and Hamas in the Gaza Strip, to heat up Israel's northern and southern borders. American soldiers based in the Persian Gulf might come under fire. Islamist backers of Iran could target civilians all over the world.
It also remains unclear how much damage an attack could inflict. Iran's nuclear facilities are scattered throughout the country and buried deep underground. Israeli officials concede that any attack could set back, but not destroy, Iran's nuclear ambitions.
Speaking with The Associated Press, a senior military official said Thursday that the threat is real. "If you are talking about the use of power against Iran, any kind of power, and create any damage over there, yes, it can be done," the official said, speaking on condition of anonymity under military guidelines.
Israel has attacked nuclear sites in foreign countries before. In 1981, Israeli warplanes destroyed an unfinished Iraqi nuclear reactor. In 2007, Israeli aircraft destroyed a site in Syria that the U.N. nuclear watchdog deemed to be a secretly built nuclear reactor.
While Israel is unlikely to strike without coordinating with the Americans, who maintain thousands of forces on aircraft carriers and military bases in the Gulf, Israeli officials will not make any promises to Dempsey, the officials said.
This week, Netanyahu told lawmakers that four rounds of international sanctions "have harmed the Iranians but not in a way that would stop their nuclear program." His deputy prime minister, Moshe Yaalon, expressed disappointment in a radio interview that the U.S. has delayed plans to expand sanctions, suggesting election-year considerations were to blame.
And in an interview published Thursday, the recently retired Israeli military intelligence chief claimed Iran already has all the components to build a nuclear bomb. "If the Iranians get together tonight and decide to secretly develop a bomb, then they have all the resources and components to do so," Amos Yadlin told the Maariv daily.
In a balancing message, Defense Minister Ehud Barak said Wednesday that Israel was "very far" from deciding whether to strike. And Israel and the United States this week postponed a major military exercise.
Israelis generally assess that Iran is close to acquiring the expertise and know-how to build a bomb but a year or two away from being able to build and deliver an atomic weapon.
In a possible preview of Dempsey's message, a senior U.S. State Department official convened Israeli journalists on Wednesday and insisted American sanctions have been effective, Israeli newspapers reported.
The official, who was not identified, reportedly said sanctions were gradual to avoid a sudden jump in oil prices but could be ramped up to include an embargo on Iran's central bank _ and were already having a harsh effect on Iran's economy.
For more than three years, Tehran has blocked International Atomic Energy Agency attempts to follow up on U.S. and other intelligence alleging covert Iranian work on nuclear arms, dismissing the charges as baseless and insisting all its nuclear activities were peaceful. In November the IAEA issued a report saying some of Iran's alleged experiments have no other purpose than developing nuclear weapons.
In Paris, French Foreign Minister Alain Juppe said he hoped European Union foreign ministers will reach an accord at a meeting Monday in Brussels on an embargo on Iranian petroleum exports and a freeze on the assets of the Iranian Central Bank.
The U.S. last month enacted similar sanctions, though it has delayed implementing them for at least six months in fear of sending oil prices higher at a time when the global economy is struggling. Iran has threatened to close the strategic Strait of Hormuz in response to sanctions.
At the Pentagon on Wednesday, U.S. Defense Secretary Leon Panetta said the U.S. military was "fully prepared" to deal with any Iranian effort to close the Strait of Hormuz. Iran has threatened to close the strategic waterway, the route for about one-sixth of the global oil flow, because of new U.S. sanctions.