Is Iran next? The calculus of military strike.

Time and again this week, President Bush and his team reiterated their position on Iran's nuclear program: America wants a diplomatic solution, and any suggestion it is moving toward an inevitable strike on Iran is "wild speculation."

At the same time, however, Mr. Bush has remained steadfast in his statements that a nuclear Iran is unacceptable and "no option is off the table" to prevent it.

The news Tuesday that Iran is now producing enriched uranium for atomic reactors - considered a first step toward nuclear weapons - has heightened the sense that America and Iran are on a collision course. A new article in The New Yorker claims that the administration is again on a path to war.

Yet amid the tumult is an effort to shape a debate that's more robust than the one before the Iraq war. While military action doesn't appear certain, the hint of it raises questions on the use of force, and what it might - and might not - accomplish.

It seems likely that precision airstrikes could set Iran's nuclear program back at least a year and perhaps several. Whether that delay is worth the probable consequences - the strengthening of a despotic regime within Iran and the increased likelihood of terrorism in nearby Iraq and the broader region - is what's at issue.

"The military option has a lot of costs," says Michael Rubin, an Iran expert at the American Enterprise Institute here. "But is the cost of the Islamic Republic of Iran having a nuclear weapon greater?"

Reports out of Iran Tuesday suggested that the country has moved closer to being able to produce a nuclear weapon. Tuesday's announcement claimed that Iran now has 164 centrifuges, which yield more-concentrated uranium. Iran would need thousands of centrifuges to produce enough fuel for a nuclear weapon - and the country's leaders insist that the program is solely for nuclear power - but it is a concern for international officials.

Few security analysts think Iran would actually use a nuclear weapon against the United States. It is an established nation motivated by self-preservation as much as power.

Indeed, Iran's terrorist links are capable of causing much more damage than they do.

But Iran does not desire to prompt the US or Israel to a major response, says Stephen Biddle of the Council on Foreign Relations. "If Iran used a nuclear weapon against New York - or if it could be traced back to Iran - Tehran would fall ... and the Iranians know that."

More likely, Iran would ratchet up its terrorist activities, knowing that enemies would be less inclined to retaliate strongly against a nuclear foe. For Dr. Rubin, that still makes a military strike "the lesser of two evils" if diplomatic efforts fail.

With the United States Army fully engaged in Iraq and Afghanistan, airstrikes against Iran's nuclear facilities are the most likely option. The operation might take five days, says retired Air Force Col. Sam Gardiner, who participated in a war game on the subject in late 2004.

Some sites, like the centrifuge facility in Natanz, are obvious and would be relatively easy to target. Others are less known or more deeply buried, leading to speculation that the United States might use special nuclear weapons designed to penetrate deep into fortified bunkers.

While that remains a possibility, Jack Straw, the British foreign secretary, called the suggestion "completely nuts," and analysts agree it would be disastrous for American interests in Middle East.

The use of conventional weapons is problematic enough. Not only do experts like Colonel Gardiner question whether America could locate and destroy all the relevant targets, but they also wonder whether even a successful attack is worth the cost.

"None of [the military options] are any good," says Gardiner.

No matter how precise or limited, any airstrike against Iran is likely to be perceived there as a declaration of war. "There is a tendency to think of it as a quick, surgical action short of war," says Dr. Biddle. "That is a mistake."

Surely, Iran would retaliate through a more aggressive terrorism campaign, he and others say, and with US troops close at hand in Iraq, they could become the first targets. Iran could also try to close the narrow Strait of Hormuz - through which all Persian Gulf traffic, including oil tankers, must pass.

In some ways, though, the greatest effect could be within Iran itself. For years, a younger generation seeking democratic reforms has struggled against Iran's government of autocratic clerics, who espouse the destruction of America and Israel.

Yet unlike Iraq, a splintered country that was essentially the creation of British imperialism, Iran has a national history stretching back thousands of years to the days of the Persians. As in any country, an attack from a foreign power would likely rally support for the government.

"Iranians are fiercely nationalistic," says Rubin.

He believes the US could mitigate that somewhat by also attacking symbols of the regime's repression, such as the ministry of information and the guard towers in the country's most infamous political prison.

Others, however, see a different lesson from history. When America helped topple Iran's government in 1953, Iranian outrage spawned the hostage crisis of 1979. Now, the US and Iran could be on a course again to poison their relations for a generation.

The concern is that the US might attack before all other options have been exhausted. Indeed, America and Iran still don't talk to each other diplomatically; they rely on Europe as a mediator.

Given that Iran is surrounded by American troops - in Afghanistan to the east and Iraq to the west - some suggest that there may still be a diplomatic way forward: A direct US offer to Iran of security guarantees for cooperation with its nuclear program.

Says Robert Hunter, a former US ambassador to NATO: "If you try and fail, at least you have a circumstance that clarifies the issue."