Why would Iran, a country that has some of the world's largest reserves of fossil fuels, need an extensive, multibillion-dollar program of nuclear development? Since the prerevolutionary years of the Shah, the determination of this country to build nuclear power plants has aroused wide suspicion.

But now, a series of revelations and new findings during the last year has left little doubt that Iran has been secretly engaged in an extensive program aimed at making and working with material that can be used in nuclear weapons. Indeed, the Iranians have been assembling the nuclear wherewithal with a speed and determination not seen since the heyday of Iraq's infamous nuclear weapons program of the 1980s.

Iran's quest—occurring in a region radically transformed by global terrorist networks and suicide tactics, which are fueled by deep-rooted hatreds and intractable grievances—tests the will of the international community to block weapons development by non-nuclear nations. And at the center of that test will be a revamped, more aggressive International Atomic Energy Agency, the Vienna, Austria-based arm of the United Nations that monitors compliance with the Nuclear Non-Proliferation Treaty (NPT). It is the IAEA that must determine whether Iran is truly cleaning up its act or whether drastic international action is necessary—a job that is stretching its resources and resourcefulness to the limit.

Since the 1991 Gulf War, the agency has been quietly transforming itself, as fast as a bureaucracy of 2200 can, to burnish a reputation tarnished by its failure in the 1980s to detect Saddam Hussein's once-huge secret nuclear weapons program. On a visit to the IAEA in April, this reporter, who worked there as an intern three decades ago, found an organization much more energetic than the sleepy backwater it was in June 1974, even after India's test of a so-called peaceful nuclear explosive just the month before.

Basically, the IAEA operates the world's most elaborate tripwire system: when a country takes steps to obstruct or impede inspections, or has not reported something it should have reported, or is found doing something it claimed it wasn't doing, that trips an alarm. Today, at IAEA headquarters, it's as if sirens were blaring and red lights were flashing all over the building.

The Iaea'S Key Findings about Iran are in reports released in March 2004 and November 2003, with the next important one due this month. In November, the IAEA concluded that Iran's nuclear program consists of practically everything needed to fuel a reactor or in effect to produce materials for bombs, "including uranium mining and milling, conversion, enrichment, fuel fabrication, and heavy water production."

Further, the November report said, following up on allegations first made by Iranian dissidents the year before, "Iran has now acknowledged that it has been developing, for 18 years, a uranium centrifuge enrichment program, and, for 12 years, a laser enrichment program."

In short, the director general told the IAEA board, summarizing the agency's findings, "It is clear that Iran has failed in a number of instances over an extended period of time to meet its obligations [under the NPT]."

The IAEA reports are remarkably detailed, blunt, and damaging, considering that they emanate from an organization that has been fighting a reputation for bureaucratic torpor for decades [see box, "Can They Agree?"]. The most disturbing of the revelations are those concerning Iran's enrichment capabilities. Its assets, at Natanz, include a centrifuge pilot plant capable of churning out about 12 kilograms of bomb-grade material a year—not quite enough for a simple bomb—as well as a large, commercial-scale plant still under construction. The larger plant, to be situated in a hardened bunker 20 meters underground, could produce as much as half a ton to a ton of weapons-grade material a year [see photo, "Spin Cycle"]. Iran is also known to have operated a more technologically sophisticated laser-enrichment pilot plant a few years ago, producing small amounts of lightly enriched uranium.

Ironically, had Iran declared all those activities to the IAEA and allowed inspectors to inspect the materials, nothing it did would have been illegal under the terms of the NPT, which guarantees members the right to pursue all plausible peaceful nuclear activities. So why did it keep so many of its activities secret, getting itself into hot water now? "Because it's a nuclear weapons program," says Robert Einhorn—the U.S. State Department's top proliferation specialist in the Clinton administration—with an air of stating the obvious.

In their defense, Iranian officials [see photo, "Power Trio "] argue that they have conducted some nuclear activities secretly because they are under economic embargo and subject to preemptive strikes from hostile countries like Israel and the United States. They often have responded petulantly to the IAEA's intrusive queries, asking why such a fuss is being made over tiny quantities of suspect materials, none actually ready for use in a nuclear weapon. They insist that they just want to be able to fuel a 1000-megawatt power reactor being built with Russian assistance at Bushehr.

But none of that really explains satisfactorily why they felt everything had to be done in secret and in clear violation of treaty commitments. "The pattern and scope of [Iran's] violations have been quite unique in the agency's experience," a senior safeguards manager at the IAEA told IEEE Spectrum.

The Critical Elements of Iran's nuclear program include not just the enrichment plants at Natanz but also plans to start building this month a 30—40–MW natural-uranium-fueled, heavy-water research reactor, with all associated equipment. The reactor could produce weapons-grade plutonium, although Iranian officials insist it will be used only to produce isotopes for medical andindustrial purposes.

Last October, when the foreign ministers of England, France, and Germany paid an emergency visit to Tehran, the Iranian leadership agreed to suspend construction of the commercial-scale enrichment plant, which would have had 50 000 centrifuges. If Iran used just a fraction of that capacity to produce weapons-grade uranium, it could get enough fissile material for several atomic bombs per year, points out David Albright, president of the Institute for Science and International Security, in Washington, D.C.

The IAEA says Iran did not agree last October to change plans for the heavy-water reactor, which Iran says is needed to replace a reactor going out of service. When complete, the plant could be fueled and operated without any foreign assistance or supplies, and, if optimized for production of weapons-grade plutonium, it could produce enough material for roughly one atomic bomb per year.

In the meantime, IAEA inspectors have found some evidence that could suggest actual weapons-related work, but it is tenuous. More seriously, it has found traces of uranium enriched to higher levels—34 and 56 percent uranium-235—than is consistent with Iran's latest declarations. Those levels are considerably higher than the 2 or 3 percent enrichment typical of power-reactor fuel. Iran's leadership, queried on the subject, claims that the traces came into the country as contamination on used nuclear processing equipment supplied by the underground Pakistani network masterminded by A.Q. Khan [see box, "Unprecedented Collusion"]. Khan, now exposed and defanged, stole European centrifuge technology, made it the basis of Pakistan's nuclear weapons program, and then sold it worldwide, apparently for profit.

So a main focus of IAEA inspection efforts during the past two months has been to determine whether the various enrichment levels of the uranium particles found in a number of places in Iran are consistent with the enrichment levels usual in Pakistan's program. To reach a conclusion, the agency needs to know more about Pakistan's activities and acquire environmental samples in Pakistan, which prompted an unusual in-person request by IAEA Director General Mohamed ElBaradei to President George W. Bush in mid-March. ElBaradei wants the United States to lean harder on its shaky ally in the battle against terrorism to provide the needed information.

Bizarrely, if the IAEA is able to conclude that the enriched uranium particles indeed originated in black-market deals between Pakistan and Iran, that will be the good news. The bad news will be if it turns out that Iran enriched the uranium itself, contrary to its latest supposedly complete and honest declarations, in which it claims not to have actually done any enrichment. If the IAEA becomes convinced that Iran produced the material itself, the agency will have little choice but to go to the U.N. Security Council for action, the logical consequences being new international sanctions against Iran, defiance on the part of Iran's leadership, and then Iran's withdrawal from the NPT. Freed from those treaty obligations, Iran would surely present a problem considerably worse than the one the IAEA and its lead member states are struggling with today.

The Iaea'S Ability To Cope with the demands now being put on it was decisively affected by the first Gulf War, which led to the revelation—utterly contrary to the agency's expectations—of Iraq's huge secret nuclear weapons program. The impact on the agency, says one of its senior legal specialists, was "like a religious experience that makes you change faith."

The most important single effect was the agency's formulation of the so-called additional protocol. Drawing on language in the basic IAEA safeguards implementation document but stretching it to the limit, the additional protocol gives inspectors the right to conduct "short-notice" inspections of any site in a member state that they consider suspect. It also allows them to take environmental samples anywhere they go—swabs put in carefully labeled and coded sealed plastic bags—that are then analyzed in a state-of-the-art clean-room laboratory set up in 1995 at Seibersdorf, Austria, about a half hour from agency headquarters. Using such devices as electron scanning microscopes and mass spectrometers, researchers can evaluate the little wipes, zero in on areas, and even lift tiny particles for the closest scrutiny.

Iran agreed to the additional protocol in October, when the three European foreign ministers persuaded it to suspend its enrichment activities. But even with the protocol in effect, not to speak of when it is not, undeclared activities are not easily detected. IAEA officials were just as surprised as everybody else when Libya's Muamar Qadafi revealed an ambitious nuclear weapons program last December.

Is the agency up to catching the determined cheater? That's a complicated question. Whereas the agency once confined its activities to single-minded verification of declarations by member states, it now draws on every kind of human and technical intelligence to try to get a bead on whether parties are conducting activities other than those declared. It employs scientific, technical, political, legal, and intelligence specialists along with the nuclear material trackers who are its lifeblood.

Still, though the agency has considerable depth of expertise in areas of traditional concern such as uranium enrichment, its broader intelligence capabilities are growing from a small base. It has no more than three experts on weapons design, for example, according to Bob Kelley, a senior safeguards manager who was deputy head of the Iraq action team.

Catching the single-minded cheat is an even taller order now that nuclear-prone states and loose-cannon organizations have been colluding and cooperating in efforts to acquire weapons-related technology. With North Korea trading missile technology for nuclear know-how, and Pakistanis having provided personnel, materials, equipment, and blueprints to any properly credentialed Islamic customer, might such parties deal not just in material for, say, a dirty bomb, but in actual working atomic bombs? "The possibility cannot be excluded," a senior safeguards official said, speaking in a level voice.

That's also the view of Leonard Spector, a proliferation expert at the Monterey Institute of International Studies' branch office in Washington, D.C., who used to produce a highly regarded annual report on proliferation for the Carnegie Endowment in Washington. Spector told Spectrum that it is not paranoid to wonder, for example, whether a rogue unit in Pakistani intelligence might sell or give Iran a bomb, or whether Iran might turn over a nuclear weapon to friends in Hezbollah, the Lebanese group it has sponsored, colluding in terrorist assaults on U.S. military installations [see box, "More Dangerous Than Ever "]. Remember, he says, "a stated reason for the Iraq war was the possibility of Saddam's providing a nuclear weapon to a terrorist group."

Those Who Would Dismiss such sobering thoughts are not much helped by some of the rhetoric coming out of Tehran. Two years ago, in a "sermon" delivered at Tehran University on 14 December, the former Iranian president Akbar Hashemi-Rafsanjani said, "If one day...the world of Islam is mutually equipped with the kind of weapons which Israel presently possesses, the world's arrogant [colonialist] strategy will then come to a dead end, because the use of an atomic bomb on Israel won't leave anything; however, in the world of Islam [use of a bomb] will just cause harm, and this scenario is not far-fetched." (The speech can be found on the Web in several alternative translations.)

No doubt with such inflammatory rhetoric in mind, as well as the basic trends discussed here, ElBaradei has said in interviews, columns, and speeches over the last year that unless there is a fundamental change of course, the Middle East is headed for a nuclear catastrophe. He'd like to see it made a nuclear-weapons-free zone—like South America or Africa—and he'd like to put big nuclear materials facilities, like those being constructed in Iran, under multinational or international management.

Regrettably, however, there is little or no hope of a new nuclear-free zone being created. Could Israel be persuaded to give up what it sees as its last-ditch defense? And as long as it does not, will there not be Islamic states determined to assemble the wherewithal to match it kiloton for kiloton? As for the idea of multinational facilities, it's not easy to imagine what parties would be suitable partners for Iran in ownership of such facilities, or that Iran would agree to cede control over facilities it sees as its ticket to a seat at the nuclear table.

What ElBaradei also would like to see, and what's a little more imaginable, is for the United States to engage in a more intense and constructive dialogue with Iran's leadership. In the absence of that, says his spokesman Mark Gwozdecky, "it will be hard to keep this situation from just careening from one crisis to another."