WASHINGTON -- Should Israel decide to launch a strike on Iran, its pilots would have to fly more than 1,000 miles across unfriendly airspace, refuel in the air en route, fight off Iran's air defenses, attack multiple underground sites simultaneously -- and use at least 100 planes.
That is the assessment of American defense officials and military analysts close to the Pentagon, who say that an Israeli attack meant to set back Iran's nuclear program would be a huge and highly complex operation. They describe it as far different from Israel's "surgical" strikes on a nuclear reactor in Syria in 2007 and Iraq's Osirak reactor in 1981.
"All the pundits who talk about 'Oh, yeah, bomb Iran,' it ain't going to be that easy," said Lt. Gen. David A. Deptula, who retired last year as the Air Force's top intelligence official and who planned the American air campaigns in 2001 in Afghanistan and in the 1991 Gulf War.
Speculation that Israel might attack Iran has intensified in recent months as tensions between the countries have escalated. In a sign of rising American concern, Tom Donilon, the national security adviser, met with Prime Minister Benjamin Netanyahu of Israel in Jerusalem on Sunday, and the chairman of the Joint Chiefs of Staff, Gen. Martin E. Dempsey, warned on CNN that an Israeli strike on Iran right now would be "destabilizing." Similarly, the British foreign secretary, William Hague, told the BBC that attacking Iran would not be "the wise thing" for Israel to do "at this moment."
But while an Israeli spokesman in Washington, Lior Weintraub, said the country continued to push for tougher sanctions on Iran, he reiterated that Israel, like the United States, "is keeping all options on the table."
The possible outlines of an Israeli attack have become a source of debate in Washington, where some analysts question whether Israel even has the military capacity to carry it off. One fear is that the United States would be sucked into finishing the job -- a task that even with America's far larger arsenal of aircraft and munitions could still take many weeks, defense analysts said. Another fear is of Iranian retaliation.
"I don't think you'll find anyone who'll say, 'Here's how it's going to be done -- handful of planes, over an evening, in and out,' " said Andrew R. Hoehn, a former Pentagon official who is now director of the Rand Corporation's Project Air Force, which does extensive research for the United States Air Force.
Michael V. Hayden, who was the director of the Central Intelligence Agency from 2006 to 2009, said flatly last month that airstrikes capable of seriously setting back Iran's nuclear program were "beyond the capacity" of Israel, in part because of the distance that attack aircraft would have to travel and the scale of the task.
Still, a top defense official cautioned in an interview last week that "we don't have perfect visibility" into Israel's arsenal, let alone its military calculations. His views were echoed by Anthony H. Cordesman, an influential military analyst at the Center for Strategic and International Studies in Washington. "There are a lot of unknowns, there are a lot of potential risks, but Israel may know that those risks aren't that serious," he said.
Given that Israel would want to strike Iran's four major nuclear sites -- the uranium enrichment facilities at Natanz and Fordo, the heavy-water reactor at Arak and the yellowcake-conversion plant at Isfahan -- military analysts say the first problem is how to get there. There are three potential routes: to the north over Turkey, to the south over Saudi Arabia or taking a central route across Jordan and Iraq.
The route over Iraq would be the most direct and likely, defense analysts say, because Iraq effectively has no air defenses and the United States, after its December withdrawal, no longer has the obligation to defend Iraqi skies. "That was a concern of the Israelis a year ago, that we would come up and intercept their aircraft if the Israelis chose to take a path across Iraq," said a former defense official who asked for anonymity to discuss secret intelligence.
Assuming that Jordan tolerates the Israeli overflight, the next problem is distance. Israel has American-built F-15I and F-16I fighter jets that can carry bombs to the targets, but their range -- depending on altitude, speed and payload -- falls far short of the minimum 2,000-mile round trip. That does not include an aircraft's "loiter time" over a target plus the potential of having to fight off attacks from Iranian missiles and planes.
In any possibility, Israel would have to use airborne refueling planes, called tankers, but Israel is not thought to have enough. Scott Johnson, an analyst at the defense consulting firm IHS Jane's and the leader of a team preparing an online seminar on Israeli strike possibilities on Iran, said that Israel had eight KC-707 American-made tankers, although it is not clear they are all in operation. It is possible, he said, that Israel has reconfigured existing planes into tankers to use in a strike.
Even so, any number of tankers would need to be protected by ever more fighter planes. "So the numbers you need just skyrocket," Mr. Johnson said. Israel has about 125 F-15Is and F-16Is. One possibility, Mr. Johnson said, would be to fly the tankers as high as 50,000 feet, making them hard for air defenses to hit, and then have them drop down to a lower altitude to meet up with the fighter jets to refuel.
Israel would still need to use its electronic warfare planes to penetrate Iran's air defenses and jam its radar systems to create a corridor for an attack. Iran's antiaircraft defenses may be a generation old -- in 2010, Russia refused to sell Iran its more advanced S-300 missile system -- but they are hardly negligible, military analysts say.
Iranian missiles could force Israeli warplanes to maneuver and dump their munitions before they even reached their targets. Iran could also strike back with missiles that could hit Israel, opening a new war in the Middle East, though some Israeli officials have argued that the consequences would be worse if Iran were to gain a nuclear weapon.
Another major hurdle is Israel's inventory of bombs capable of penetrating the Natanz facility, believed to be buried under 30 feet of reinforced concrete, and the Fordo site, which is built into a mountain.
Assuming it does not use a nuclear device, Israel has American-made GBU-28 5,000-pound "bunker buster" bombs that could damage such hardened targets, although it is unclear how far down they can go.
Earlier this month, a Bipartisan Policy Center report by Charles S. Robb, the former Democratic senator from Virginia, and Charles F. Wald, a retired Air Force general, recommended that the Obama administration sell Israel 200 enhanced GBU-31 "bunker busters" as well as three advanced refueling planes.
The two said that they were not advocating an Israeli attack, but that the munitions and aircraft were needed to improve Israel's credibility as it threatens a strike.
Should the United States get involved -- or decide to strike on its own -- military analysts said that the Pentagon had the ability to launch big strikes with bombers, stealth aircraft and cruise missiles, followed up by drones that could carry out damage assessments to help direct further strikes. Unlike Israel, the United States has plenty of refueling capability. Bombers could fly from Al Udeid air base in Qatar, Diego Garcia in the Indian Ocean or bases in Britain and the United States.
Nonetheless, defense officials say it would still be tough to penetrate Iran's deepest facilities with existing American bombs and so are enhancing an existing 30,000-pound "Massive Ordnance Penetrator" that was specifically designed for Iran and North Korea.
"There's only one superpower in the world that can carry this off," General Deptula said. "Israel's great on a selective strike here and there."
Scott Shane contributed reporting.
This article originally appeared in The New York Times .