WASHINGTON A U.S. military strike on Iran's nuclear facilities could set Tehran's program back years but would raise the risk of retaliation against American troops in the region and of driving Iran to work even harder to make atomic weapons, U.S. experts and officials say.
Any U.S. attack -- something the Pentagon insists is not planned but is subject of frequent speculation as Iran defies calls to rein in its nuclear program -- could involve thousands of sorties and missile launches against hundreds of targets.
It would be limited to air strikes, rather than a full-scale attack requiring U.S. ground forces, who are now tied down in Iraq and Afghanistan, analysts said.
But the strike would be hampered by a lack of intelligence on the number and location of the nuclear facilities dispersed throughout Iran, according to nuclear security experts.
At best, many experts say a U.S. strike could delay Iran's nuclear weapons capability by three to five years. Parts of the program would likely survive, perhaps even critical technologies and certainly know-how.
"We could set it back probably at least several months maybe a few years but then we run the risk of stimulating them to work even harder next time, burying facilities even deeper, putting in more air defence batteries," said Charles Ferguson, nuclear expert at the Council on Foreign Relations think tank.
The United States and others accuse Iran of seeking to develop nuclear weapons under the cover of a nuclear energy program. Tehran denies the charge.
While U.S. officials say they do not plan an attack, they will not take the option of military action off the table.
Some analysts say Israel, which Tehran has threatened with destruction, is more likely to strike Iran than the United States, especially if Washington does not act before the end of President George W. Bush's term in January.
White House spokeswoman Dana Perino on Wednesday dismissed as rumour the suggestion that Israel was trying to persuade the administration to take military action before Bush exits.
"President Bush believes that we can solve this issue diplomatically, and that everyone's preference is to solve it diplomatically, not just here in the United States but with our allies and certainly with Israel," she said.
But bellicose rhetoric in the past and close encounters between U.S. and Iranian ships in the Gulf have driven speculation in the oil markets that the United States could launch a strike before Bush's term ends.
Potential targets most often cited by nuclear experts include three large-scale facilities -- the underground Natanz uranium enrichment facility, the Arak plant that could be used to produce plutonium and a major nuclear research centre and uranium conversion facility at Isfahan.
Other facilities are scattered throughout the country and could be included as targets, experts speculated. Satellite pictures suggest Iran has dug tunnels around Natanz, for example, which could contain uranium enrichment equipment.
Nuclear research facilities in Iran's capital might be targeted as well, but such strikes raise the risk of civilian casualties and the attendant risk of international uproar, said U.S. defence officials, speaking on condition of anonymity.
RISK OF RETALIATION
The military risks, however, are high, according to both defence analysts and officials.
Primary among them is the possibility of retaliation against U.S. troops by Islamist militant groups Washington says Tehran supports. The U.S. military accuses Iran of training and equipping the Shi'ite militias in Iraq, which are seen by U.S. commanders as one of the largest threats in that country.
But particularly frightening to officials inside the Pentagon is the possibility Iran would use suicide boats to attack U.S. ships in the Gulf or to disrupt crude oil trade.
John Bolton, a former U.S. ambassador to the United Nations and advocate of military action against Iran, said the White House is unwilling to act, especially after a U.S. intelligence report last year said Iran stopped work on a nuclear bomb. Some hawks say that report understated the threat.
The Bush administration's "Iran policy has been shredded both diplomatically and to the point of precluding the potential use of force," Bolton told Reuters.
"With virtual certainty that the United States won't act, that forces them (the Israeli government) to a decision point on whether they will act militarily," he said.
The New York Times, citing unnamed sources, last week said more than 100 Israeli jets took part in a long-range exercise that looked to be practice for real sorties over Iran.
Israel could reach Iran in party by flying over Iraq, whose air space is controlled by the United States.
(Editing by David Storey and David Wiessler)