The administration has added Saddam Hussein's nuclear weapons program to its list of reasons why a war with Iraq may be necessary. This new justification was cited after polls showed it to be the only motive for fighting supported by a majority of Americans. Since the administration had until recently been relaxed to the point of offhandedness about Iraq's nuclear activities, critics have naturally enough claimed that the threat is now being exaggerated. This prompts angry countercharges from the Saddam-as-Hitler group, and the whole issue is becoming muddled at a time when clear thinking is more than usually valuable.

There can be no doubt that Iraq is trying to become a nuclear weapons state. That has been clear at least since 1980, and some would say since 1976, when Iraq purchased the Osiraq research reactor from France. When asked why a party to the Non-Proliferation Treaty would want such a large facility, Iraq said it needed to produce medical radioisotopes. In 1980 Iraq attempted to buy 25,000 pounds of depleted uranium, which could have no other use than to be irradiated inside Osiraq to produce plutonium. After that, even the most credulous could no longer swallow the peaceful program/medical research cover story.

There are five covert ways to acquire the fissile material for a nuclear weapon, two involving highly enriched uranium (HEU), two that use plutonium and one that could use either. Iraq has pursued all five.

One can buy a research reactor and then divert its highly enriched fuel. When the Israelis bombed Osiraq, they missed 12 kilograms (about 27 pounds) of its fuel, which is enough to make a single weapon and is the source of concern behind the estimates that Iraq might have a bomb in six to 12 months. According to the International Atomic Energy Agency, which inspects this suitcase-sized material twice a year, it could actually be readied for weapons use in one to three weeks (assuming the rest of the bomb is ready).

One can also build a centrifuge enrichment plant, buy uranium and then enrich it to weapons grade. This was the route Pakistan followed in its successful covert program. Such plants require materials and components that have few other uses, which Iraqi agents and front companies have been aggressively shopping for worldwide. However, building a large enough enrichment plant is no small undertaking. Intelligence estimates have generally concluded that it will take five to 10 years for Iraq to acquire weapons this way.

One can produce plutonium either by irradiating natural or depleted uranium in a research reactor, as Iraq attempted with Osiraq, or one can build a reprocessing plant. Iraq bought a laboratory scale reprocessing unit from Italy in the mid-'70s and tried to buy a full-sized one. But, like Pakistan, it now seems to have pinned its hopes on enrichment.

Finally, one can buy HEU or plutonium on the black market if it can be found, or one can steal it, probably from a civilian facility where security may be lax. Sting operations have shown that Iraq has tried to do the former, though without success. The latter belongs in the category that worries some experts most -- what Iraq may have that we don't know about. There is no evidence that such a theft has occurred in Iraq's case, but the possibility is not farfetched. It may have been the route by which Israel acquired its first HEU -- from an American facility.

Making a nuclear weapon entails a lot more than acquiring the fissile material, however. Iraq's sophisticated missile program can be taken as evidence that its technicians could be equal to the task, though not that they are ready today. Saddam's use of chemical weapons shows unequivocally that he is prepared both to use weapons of mass destruction and to violate treaty commitments in doing so.

The question remains whether any of this is relevant to the choice of whether to attack soon or to wait and see if sanctions will work. A military solution to either the immediate (one-week to one-year) threat or to the five-to-10 year possibility requires that intelligence be able to pinpoint where in Iraq the nuclear materials and facilities are (key components have certainly been scattered to as many sites as possible). If U.S. intelligence were that good, there would be much more certainty about the nature of the threat. There must also be high confidence that air strikes can destroy everything completely, including underground laboratories. The 1981 Israeli raid on Osiraq was a textbook example of pinpoint bombing, yet one weapon's worth of nuclear fuel remains. Inflicting permanent damage to the key facilities would probably require extensive use of ground troops in Iraq.

And what if sanctions force Iraq out of Kuwait? If, as the bulk of the evidence seems to suggest, Saddam still needs many items from abroad, the present crisis may improve the chances of stopping him. Nations that have supported his various programs with financial or technical assistance -- including Brazil, Egypt, Saudi Arabia and Kuwait -- are not likely to do so again. Pakistan and China would be questionable, but international pressure and greater scrutiny could certainly be brought to bear. European countries where companies have inadvertently or knowingly made key exports -- including Germany, Switzerland and others already mentioned -- would presumably intensify their efforts to prevent any further sales.

If Saddam were to make and use a single bomb from his 12.5 kilos of HEU, he would be choosing national suicide. A U.S. attack might prevent that from happening, though such a small amount of material could be hidden by the Iraqis or smuggled to safety. Against the far more serious risk that Iraq is attempting to build a militarily significant nuclear arsenal, sanctions appear to be at least as effective as a military attack. There may be other reasons to opt for war over sanctions, but public opinion polls notwithstanding, the nuclear threat is not a strong one.