The question hanging over Washington for months has been this: Will Israel strike the Iranian nuclear program?

The Obama administration seems to have bought some time this week after rounds of meetings and speeches with Israeli officials in Washington.

Still, the president assured Israeli Prime Minister Benjamin Netanyahu that the U.S. will do all in its power to prevent Iran from acquiring a nuclear weapon.

So the military option is still on the table.

Obama talked tough this week and made it clear that the nuclear program that Iran insists is for civilian use will never be permitted to develop weapons.

"We will not countenance Iran getting a nuclear weapon," the president said.

Not much ambiguity there. The question is what would the U.S. do if it decided that military action was necessary.

There is not just one military option.

Israel could act on its own. It could send waves of planes, American-made F-15s and F-16s, to attack Iran's nuclear sites. They might get just one chance at their targets.

The Israelis have first-rate military capabilities, says retired Air Force Lt. Gen. Dave Deptula.

Deptula, who designed the U.S. air campaign for the 1991 Persian Gulf War, notes that Israeli warplanes successfully destroyed an Iraqi nuclear site in 1981 and another in Syria in 2007.

Iran Would Be A Tough Target

But Iran is a much more difficult military challenge that involves dozens of potential targets, he says.

In addition, Iran's secretive program is at least partially shielded under mountains.

"So a certain enrichment capacity, a certain hiding of facilities, a certain impenetrability of Iranian facilities would already be a reason to move militarily," says Daniel Levy, a former Israeli government official who's now at the New America Foundation.

For all these reasons, Israel might want to move sooner rather than later. But these are also reasons Israel might not succeed without U.S. help.

For an attack on Iran, Deptula says, the Israelis just don't have enough aircraft or the right warplanes.

"There is a capacity issue," he says. "The number of aim points or target points that one would want to respond against is relatively large ... to set back the program a significant period of time."

Most defense analysts, like Dan Goure of the Lexington Institute, say any Israeli strike might set back Iran's program by no more than a year or two. Israel might have a sophisticated air force, but not the kind needed to destroy Iran's nuclear program.

"They don't have the aircraft to carry the really big bombs," he says.

Big Bombs Require Big U.S. Planes

Israeli planes can carry 2,000-pound bombs. The Americans have 30,000-pound bombs designed to eliminate the type of underground facilities Iran has constructed. Goure says only the Americans have the planes that can carry those enormous bombs.

"You need a bomber, you'd need a B-52, a B-2 bomber to carry something that massive," he says.

Daniel Levy says that's what Israel would like to see: American bombers heading toward Iran. He says Israeli leaders know they can't destroy Iran's nuclear program on their own, they can only delay it.

"I think the focus from Israel's perspective is still more on how do you walk America further down the road to almost inevitable conflict rather than any immediate Israeli action," he says.

Deptula says even for the U.S., any air campaign against Iran would be a long, complex operation.

"This is not a walk in the park," he says. "It would require an orchestrated campaign of some duration, weeks not days, against a wide variety of very challenging target sets."

Deptula says those who talk lightly of airstrikes and bombing need to answer this question: What are you trying to achieve? If it's halting Iran's nuclear program for good, it may take more than air strikes.

"To eliminate the program, one then has to address how far are you willing to go in terms of removing and replacing the regime," he says.

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