Can their program be destroyed? The military options against the mullahs.

AT Natanz, about 130 miles from Tehran, the Iranian regime is constructing a vast "commercial scale" uranium-enrichment facility that will house as many as 55,000 centrifuges. Deep under several meters of steel-reinforced concrete, conveniently out of reach of the most powerful known conventional bunker-busters, the facility will be able to produce sizeable quantities of lightly enriched uranium (LEU) in a matter of months once it is operational. The steps required to enrich LEU all the way to highly enriched, weapons-grade uranium are few and have been described by experts as purely mechanical.

Some have argued that operational launch of these main "enrichment cascades" at Natanz, which could occur next year, should in and of itself be considered a red line by U.S. officials--i.e., a line Iran must not be permitted to cross. But Iran is generally cooperating with inspectors from the International Atomic Energy Agency: If it continues to do so, and if the plant's operations remain transparent, the Bush administration is likely to conclude that it can hold its breath for a little while to see how things develop. It will be a nail-biting period of months; intelligence assessments will be studied nervously; allies will be consulted weekly; and the most minor IAEA inspections will be followed minutely.

Iran will be on notice--but the prize within the mullahs' reach may be just too tantalizing. In a 2004 article in Asia Times, Kaveh Afrasiabi, a Tehran University political-science professor who is close to former high-ranking officials in the regime, put Tehran's thinking starkly:

  There is an emerging "proto-nuclear deterrence" according to which
  Iran's mastery of the nuclear fuel cycle would make it "nuclear weapon
  capable" in a relatively short time, as a sort of pre-weapon
  "threshold capability" that must be taken into account by Iran's
  enemies contemplating attacks on its nuclear installations. Such
  attacks would be met by stiff resistance, born of Iran's historic
  sense of nationalism and patriotism, as well as by a counter-
  weaponization based on quick conversion of the nuclear technology.
  Hence, the longer the U.S., and Israel, keep up the military threat,
  the more powerful and appealing the Iranian yearning for a
  "proto-nuclear deterrence" will grow.

This window into the regime's thinking suggests what might happen next. If for some reason--say, a sudden increase in Mideast tensions--Iran stops cooperating with the IAEA, we will suddenly find ourselves at a point of no return. We will no longer be able to know what Iran is doing with its nuclear capabilities. The crisis will finally arrive for decision in the Oval Office, just as it did--albeit in much simpler form--for the Clinton administration, in the North Korean nuclear crisis of 1994.

A NOT-SO-DISTANT MIRROR

From January 1993 onward, the Clinton administration was keeping a close watch on North Korea's nuclear reactor at Yongbyon. The North Koreans were pursuing the plutonium route to nuclear weapons--creating a system that, once established, can produce many more nuclear weapons than the uranium method the Iranians are now using. But the plutonium route is also much easier to disrupt, because weapons-grade plutonium can be extracted only from the spent fuel of a nuclear reactor; the system is vulnerable at that point in the production chain.

Suddenly, on May 4, 1994, North Korea began to remove plutonium- laden spent fuel rods from the Yongbyon reactor. A few weeks later, IAEA director-general Hans Blix reported that the agency's ability to measure spent fuel at the facility would be lost within days if the discharge were not stopped. Then, on June 13, days before former President Jimmy Carter's visit to Pyongyang, North Korea announced its intention to withdraw from the Nuclear Nonproliferation Treaty and threatened to expel IAEA inspectors from the Yongbyon facility. Two days later, Brent Scowcroft and Arnold Kanter wrote in the Washington Post:

  As things now stand, if Pyongyang implemented such a maneuver, we
  might never know whether it had gone ahead and reprocessed enough
  plutonium for another four to six nuclear weapons.... We should tell
  North Korea that it either must permit continuous, unfettered IAEA
  monitoring to confirm that no further reprocessing is taking place, or
  we will remove its capacity to reprocess.... The approach we have
  outlined is designed to prevent a bad problem from becoming worse....
  More generally, we should ensure that both our actions and our words
  make clear to Pyongyang that we will not be intimidated by its threats
  and will not be paralyzed by the possibility of war.

In the 2003 book Going Critical, three of the Clinton-administration officials closest to the crisis recall the deliberations. "Logically," they write, "there were three military possibilities for attacking Yongbyon": destroy just the reprocessing facility; destroy the entire facility, including the reactor; or destroy the entire facility and "remove key North Korean military assets, in order to degrade Pyongyang's ability to retaliate." Cowed by North Korea's threat to unleash war against the South--an almost-obvious bluff--Clinton placed the fate of the nonproliferation regime in the hands of "unofficial" envoy Jimmy Carter, who promptly reached a deal with Pyongyang and then announced it on CNN--without telling the administration first. The administration was forced to cave on the most important U.S. demands: inspections at any time and any place, and the dismantling of the plutonium program.

The lessons of the North Korea crisis are clear. The reason Clinton considered bombing North Korea's nuclear facility at Yongbyon when it began removing spent fuel rods from the reactor pool was that this represented the last moment at which the nature and scope of North Korea's nuclear activities could be known with any certainty. They were still years away from being able to manufacture a warhead, and yet the U.S. treated Pyongyang's threat to eliminate nuclear transparency as an act of war--which, strategically speaking, is exactly what it was.

DON'T LOSE THE WINDOW

An Iranian decision to stop cooperating with the IAEA will trigger a similar crisis in the U.S. national-security establishment. The options are likely to be presented from "lightest" to "heaviest," according to a progression calibrated to anticipate Tehran's likely reaction to any military strike. The "lightest" option could consist of limited strikes on the handful of facilities directly related to uranium enrichment. The most important of these are buried deep underground at Natanz. Experts believe we could not be confident of completely destroying the facilities if we relied only on conventional air strikes, even if we resorted to repeated strikes on the same targets in the hope of creating craters within craters deep enough to reach the facilities.

Unfortunately, the alternatives to conventional air strikes are few, and they tend to the outlandish. Nuclear bunker-busters are certainly out of the question, if indeed they exist at all. Other possibilities are helicopter-borne missions using special-operations forces, and a "thunder run": a swift, heavily armed ground incursion by large-unit forces operating out of Iraq or Afghanistan.

But given the degree of skepticism attaching to the likely success of "light strikes" in setting back Iran's nuclear program, the Joint Chiefs are likely to recommend that any strikes seek to destroy Iran's nuclear program "cradle-to-grave": from uranium mining, to conversion facilities, to enrichment facilities, to hard-water plants, to the various reactors now under construction. A crucial element in these strikes would be Iran's nuclear know-how. This would mean that, for the first time in history, the offices and laboratories of university faculty may become military targets. Such a "strike package" might set Iran's nuclear program back ten years, although many experts are more pessimistic.

Because Iran's nuclear facilities are so dispersed and, in many cases, well defended, estimates of the number of possible targets for this option range from 300 to 1,500. Given these numbers, the mission could not be accomplished exclusively with stealth aircraft. Hundreds of relatively slow-moving non-stealth aircraft would be involved--so the initial phases of the operation would have to wipe out Iran's national air defenses. That in turn would mean an operation lasting many days or even weeks.

When the smoke settles, Tehran will not delay in retaliating somehow. It is likely to perceive that its room for maneuver is somewhat constrained, because while everyone knows that the U.S. is reluctant to invade Iran, an Iranian retaliation could be so serious as to force the U.S. into an all-out war. And yet there are many possible acts of retaliation Iran could commit before triggering an all-out U.S. invasion. Iran possesses a significant arsenal of long- and medium-range missiles, and could use them against countries that facilitate any U.S. action--or against Israel, as Iran has already threatened.

Iran's most fearsome counter-deterrent to the destruction of its nuclear facilities is the implied threat to ruin America's project in Iraq. But here, the U.S. has a deep strategic advantage. The success of democracy in Iraq is rapidly becoming not America's fight, but rather that of Iraq's Shiite majority--the very group that Tehran seeks most avidly and actively to protect. One of Iraq's most important Shiite political parties--the Supreme Council for the Islamic Revolution in Iraq--is a key player in the government, and it was created in Iran to fight Saddam. Thus, in order to ruin the U.S. effort in Iraq, Iran must first directly and vividly ruin the project of the very factions that are friendliest to it.

It is worth remembering, also, that a huge military force is parked on Iran's western and eastern borders. One might think that this force is largely tied down in Iraq now, but over the past year, it has slowly withdrawn from large-scale forward operations. In a sense, Iran's nuclear program may now be in a race against time, while America's assets and options multiply.

Furthermore, Iran's military is surprisingly weak. Its army has on the order of 300,000 troops, covering a country four times the size of Iraq. It would never be able to stop the advance of a single American mechanized or armored brigade on a "thunder run." The country is, tactically speaking, essentially wide open for military operations of many kinds. It was perhaps because of this that, reportedly, some of Iran's most senior generals recently wrote a letter to Ayatollah Ali Khamenei warning that Ahmadinejad was embarking on a dangerous course of action, and that Iran could not risk war with the U.S.

Beyond military retaliation, Iran might launch a worldwide terror campaign against America. The regime claims that the Revolutionary Guards have established a "Lovers of Martyrdom Garrison" of suicide bombers for this very purpose, with thousands of recruits. But, as some experts have pointed out, one thing the current War on Terror has not seen is the phenomenon of Shiite--much less Persian--suicide bombers. Thankfully, the suicide-bombing tactic is thus far almost exclusively the domain of Sunni Arabs. With a view to the looming confrontation, Iran is also preparing to shut down the Strait of Hormuz, through which passes 40 percent of the world's oil. But the Tehran regime derives 65 percent of its revenue from oil shipments, almost all of which must pass through the Strait of Hormuz--making this, too, an unattractive option.

THE FATAL CHOICES

Taking into account Tehran's options for retaliation after any initial strike, heavier strike packages would target known missile forces, the air force, the Revolutionary Guards and other military bases, command and control, and naval assets along the Persian Gulf. The U.S. may devise its plan "backwards," from the desired result to a specific military strategy. That's what the U.S. did in Kosovo: The air campaign designed by Gen. Wesley Clark struck first at the Milosevic regime's most essential command-and-control assets. After initial operations to degrade Serbia's air defense, NATO passed immediately to the core facilities of the Defense Ministry, paralyzing the regime's military capability from the inside out. And then NATO started to remove the regime's ability to function as a state, destroying key transportation infrastructure, energy resources, and communications facilities. It did all that, and even put a cruise missile in Milosevic's bedroom, before shifting its focus to the ultimate objective: the Serbian ground forces in Kosovo.

That's what Iran will likely face. The Iranian regime has to be made to understand that in the current state of Middle East confrontation, in which many Americans have already been killed because of Iranian-inspired acts of aggression, their acquisition of a nuclear breakout capability represents a grave threat to the U.S.--and a potentially fatal threat to Israel--and that the West is grimly aware of this. Iran's nuclear advance is a dramatic escalation in an already tense regional cold war. And that, for all strategic purposes, is an act of aggression.

International law has never devised an authoritative definition of aggression. But, strategically speaking, the definition is quite clear: Any act that directly threatens the security of other states is an act of aggression. As Kofi Annan said to the General Assembly some years ago, "It is not enough to denounce unilateralism unless we also face up squarely to the concerns that make some states feel uniquely vulnerable, since it is those concerns that drive them to take unilateral action."

Irredentist powers often seek to alter the status quo in order to advance important aims. They must then typically choose between a laborious process of negotiation aimed at leaving all parties satisfied, or achieving the alteration quickly and aggressively. China, for example, has shown an increased willingness to choose the path of negotiating in good faith, even if that means deferring strategic goals that may already be within its reach unilaterally; its bid to exploit mineral claims in the South China Sea comes immediately to mind.

Iran has at times suggested that it might be willing to do this, but in fact the West's negotiations with Iran have not slowed down the regime's multi-track nuclear advance. Iran's goal in the negotiations is to provide assurances to the Europeans, regardless of whether the U.S. also accepts them--in a bid to divide the international community. Iran, in short, is not negotiating in good faith.

To insist that Iran be transparently peaceful in its nuclear activities is to insist upon the protection of the greatest benefit of the nonproliferation regime: transparency. That is the first and most important line of defense in the age of WMD. Especially in the case of hostile terror-sponsors, nuclear nonproliferation is an indispensable element of our national security. If Iran eliminates the hope of maintaining transparent nonproliferation through diplomatic means, it will force upon the United States a choice between abandoning one of the most valuable ramparts of our security--or defending it by force.

Weighing the risks and benefits of a military confrontation with Iran against the risks and benefits of avoiding one will be excruciatingly difficult. The U.S. should push that decision squarely on Iran. Iran is now the power seeking to challenge the status quo--so logically the risk calculation is in the first instance Iran's to make. The object of U.S. policy must be to increase the risks of confrontation such that they become prohibitive to Iran. And the only way to accomplish that is to send a clear message to the Iranian regime that we will not allow it to compromise our national security and push the world farther down the slippery slope of uncontrolled nuclear proliferation.

Mr. Loyola, a former consultant to the Department of Defense, is a visiting fellow at the Foundation for the Defense of Democracies.