Iran is two years to five years away from being able to produce a nuclear weapon, the former head of the U.S. weapons-hunting team in Iraq said Wednesday. But David Kay said the U.S. should not consider bombing Iranian nuclear facilities unless the weapon was about to be transferred to a terrorist group.

Kay, who led the Iraq Survey Group from 2003 until early 2004, said the U.S. should line up international support to pressure Iran to give up on a nuclear weapon, while also preparing for the strong possibility that effort will fail. Preparations could include offering security guarantees to Iran's neighbors and shoring up Middle East stability and economic growth.

Iran is 80 percent of the way to a nuclear weapon, Kay estimates, but the last 20 percent of development is the most difficult. He noted that Iran has worked on the program for 20 years without successfully producing a weapon.

"You've got a clear record of country that is damned determined at some point to develop nuclear weapons," Kay said in a talk at the Nixon Center. "The real question to ask is, `What are the political strategies we can follow now that can lessen the impact?"' of a nuclear Iran.

Iran denies it is seeking a weapon or hiding a bomb program behind its known drive to perfect nuclear technology that could be used to produce electricity. Estimates of Iran's progress vary. Western intelligence agencies generally agree that if Iran chose to, it could field a nuclear device within a few years. Iran has accelerated its uranium enrichment program this year.

Kay said there is "virtually no possibility" Iran will give up its uranium enrichment program, which can be used to fuel civilian reactors for domestic energy use as well as make fissile material for warheads.

He dismissed the notion that a U.S. or Israeli military strike on Iran's nuclear infrastructure would be effective or useful. He said it would only delay the development of a weapon by one to two years at the most, and would unite Iran's people more firmly behind its leaders.

Kay would only advocate a military attack "if I found the Iranians had transferred a nuclear weapon to a third party, a terrorist organization or another state," or if it used a nuclear weapon in an attack.

The value of diplomatic outreach to Iran has been an issue in the current presidential campaign.

Democrat Barack Obama favors direct diplomacy. He says he would meet Iran's leaders without precondition but after the proper groundwork is laid. Obama also says he would intensify diplomatic pressure on Tehran before Israel feels the need to bomb Iranian nuclear facilities.

Republican John McCain favors tougher penalties and opposes direct high-level talks with Iranian President Mahmoud Ahmadinejad. McCain's vice presidential nominee, Sarah Palin, recently said in a CBS television interview that the U.S. should not "second guess" Israel's "security efforts" against Iran.