If Iran goes nuclear ...

As recently as April, President Bush said it would be "intolerable" for Iran to possess a nuclear weapon.

Since then problems in Iraq and the presidential campaign have pried attention away from Iran's nuclear ambitions. But now the spotlight is back, intensified by new intelligence suggesting Iran is accelerating its nuclear work.

Yet Mr. Bush's recent rhetoric on the topic has been nuanced - gone is the word "intolerable." The shift may suggest two things: first, a realization that diplomatic options are limited, and second, a realization that Iran has tremendous means of influencing events in Iraq.

Despite those factors, the prospect of Iran possessing a nuclear weapon is cause for concern on several fronts, from the role that Iran's Islamic regime sees for itself in the Muslim world and the specific threat it poses to Israel, to the crucial place it holds as a global oil power. But perhaps the greatest risk is how an Iran declaring itself a nuclear power would almost certainly set off a nuclear arms race in the Middle East.

"We need to be much more worried than we have been that what we do with Iran will be a model for others," says Henry Sokolski, executive director of the Nonproliferation Policy Education Center in Washington. "The real problem of Iran is how it sets an example for others to follow in the region."

An "overtly" nuclear Iran could result in a "large nuclear crowd in the Middle East," Mr. Sokolski says: Israel would go public with the nuclear armament it has been mum about, which in turn would put tremendous pressure on Egypt to stand shoulder to shoulder in the nuclear club. Syria, Algeria, Saudi Arabia - which would feel threatened by Iran's new status - would also feel pressed to ratchet up what are assumed to be varying existing programs.

The potential impact on Israel is also key. "Right at the top I'd put what I'd call the Israel issue," says Daniel Brumberg, an Iran and Middle East expert at Georgetown University in Washington. "If Iran has an effective nuclear deterrent, its allies, particularly Hizbullah, might feel emboldened and that they have the cover to pursue a more hostile approach to Israel."

Most experts believe Iran is at least three years from actually possessing a nuclear weapon, although some believe it could get there sooner if it focused on plutonium separation rather than uranium enrichment. Another possibility is that it possesses materials and facilities the international community doesn't know about, which could also telescope that prognostication to a shorter point in the distance.

Either way, the time for heading off Iran's nuclearization is fleeting, experts say, which is one reason the issue has resurfaced. On Thursday the International Atomic Energy Agency (IAEA) is scheduled to take up Iran's case and decide whether to refer it to the Security Council - one reason Bush last week returned his attention to Iran and what he has called the problem of the world's worst regimes possessing the world's deadliest weapons.

Few observers expect the IAEA to send the Iran case to the Security Council at this point, with several European countries having just concluded an agreement with Iran to suspend its uranium enrichment programs while international assistance is negotiated.

On the heels of that agreement last week, Iran announced Monday it had frozen its uranium enrichment program. But the seeds of a breakdown appeared already sown in the deal, with Iran saying the freeze would be "brief" and tied to the Europeans' making good on promises of economic assistance, while the Europeans insisted on a "sustained" freeze before other elements of the deal would set in.

In any event, the Bush administration remains deeply skeptical of the prospects for the European plan to derail Iran's nuclear ambitions. One reason is that over recent years Iran's nuclear program has become tightly bound with national pride, thus making it all the more difficult for a regime - particularly one whose popularity is already on the wane - to give it up.

"It doesn't matter what faction it is, from the radical religious conservatives to the left, there's a consensus that Iran has a right to pursue the nuclear fuel cycle, and that indeed it has a right to develop nuclear weapons if it chooses," says Mr. Brumberg. "It's something that unites the country, so in a time of deepening divisions it's not something that anyone wants to renounce."

Ray Takeyh, an Iran expert at the Council on Foreign Relations in Washington, says the Iranians are not yet on a par with Pakistanis: "In Karachi you see clocks in the form of a nuclear warhead." But he says polls show as many as 80 percent of Iranians supporting the country's nuclear ambitions, underscoring how difficult securing an agreement from Iran may be.

Still, experts like Mr. Takeyh say it is the "exceptionalism" of the bomb landing in the hands of such an "unpredictable, unstable, and aggressive regime" that makes Iran "a nearly existential threat."

Some experts hold out the hope that Iran, if it became a nuclear power, could yet evolve in somewhat the same way India has- from a one-time international agitator to a nuclear power taking its position seriously and demonstrating stronger interests in regional stability.

That Iran has not caused all the trouble in next-door Iraq that it is assumed it could have is one factor cited in support of Iran's potential for evolving into a responsible actor. Maybe Iran would not use its nuclear status to try to drive up oil prices, or to husband a more radical Palestinian future, some observers suggest.

But even that would not address the risks posed by nuclear proliferation in perhaps the world's least stable region. As nonproliferation expert Sokolski says, the world is opening a can of worms if it allows countries the right, as Iran is claiming, to enrich uranium while claiming its ambitions are peaceful. The message to other nuclear wannabes would be clear.

The problem of everyone "becoming nuclear ready," Sokolski says, is that "maybe it's not quite the bomb, but it's within a screwdriver turn of it."