COLUMN ONE : The New, Dangerous Dominoes : Nuclear wanna-bes and wary bystanders are among nations caught in a global balancing act over who has--and who soon may get--atomic weapons. The rising number of players raises the risk of disaster.

The scenario is called “nuclear dominoes,” and it is every defense planner’s nightmare--because the first dominoes have already begun to fall.

It begins this way: North Korea succeeds in putting a nuclear warhead atop a medium-range missile--and then offers to sell similar weapons to other “outlaw states.” Or Iran buys a nuclear bomb from the arsenal of the former Soviet Union. Or Ukraine declares itself a nuclear power and keeps some of the nuclear weapons already on its territory.

Those events are not fiction; all are under way already.

The “domino effect” is what happens next. If North Korea goes nuclear, South Korea and Japan seek atomic deterrents of their own. In response to Iran’s coup, Saudi Arabia asks the United States to deploy nuclear weapons on its soil, and Israel targets Tehran with its own atomic warheads. If Ukraine stays nuclear, Russia begins rebuilding its armed forces, Germany and Poland think about atomic weapons, and Central Europe becomes a potential battleground.

Five years after the end of the Cold War, the familiar terror of the old U.S.-Soviet nuclear stalemate has abruptly been replaced by new, more unpredictable dangers: The Bomb, with its power to level cities and destroy civilizations, is passing into many more hands.

President Clinton calls it “the biggest threat we will face.”

“I spend a lot of time on this issue,” he said last year. “We have got to stop the proliferation of nuclear weapons.”

“It’s the toughest issue there is,” said Samuel W. Lewis, who recently retired as the State Department’s chief of policy planning. “It keeps people awake at night.”

Concern has been growing for more than a decade as the irresistible spread of technology made it possible for countries such as Israel, India and Pakistan to build atomic weapons on their own.

But since 1990, three unexpected events have made the problem more pressing--and more dangerous:

* The Persian Gulf War revealed that Iraq was much closer to developing nuclear weapons than the United States had realized--and showed that the United Nations’ safeguards against proliferation did not work. Before the war, U.S. intelligence knew of only two Iraqi nuclear-weapon development sites; after the war, they learned that there had been at least 20. “If that war had come a year or two later, we might have been looking at a nuclear Iraq,” one U.S. official said.

* The collapse of the Soviet Union left more than 30,000 nuclear warheads under the uncertain control of an impoverished and disintegrating military Establishment. At some point, officials fear, some of those weapons will be sold on the black market to Iran, Libya or some other eager buyer. “That’s the most frightening thing,” said David Kay, the United Nations’ former chief nuclear inspector. “I think it’s inevitable . . . that at some point we will face either the use or the threat of use of former Soviet nuclear material.”

* North Korea’s drive to develop its own nuclear weapons already has produced enough plutonium for two warheads and could soon produce enough for five more. What worries U.S. officials most is the prospect that the Pyongyang regime might sell nuclear warheads abroad, just as it has already sold medium-range missiles to Syria, Iran and possibly Libya. “North Korea is the destabilizing factor,” a senior U.S. official said. “We are at a turning point with that one.”

The potential sale of nuclear weapons from North Korea or the former Soviet Union raises an entirely new threat, what one official calls a “blowout” in the non-proliferation system. In the past, a country that wanted nuclear weapons had to spend years assembling nuclear material and warhead technology. Now, with enough money and the right connections, any country--perhaps even a terrorist group--could simply buy a nuclear arsenal “off the shelf.”

If that happens, many more countries will want nuclear weapons--if only to protect themselves against “outlaw nations” such as North Korea and Iran.

And, in time, they will get them.

“Countries who want the technology bad enough will eventually get it,” Lt. Gen. James Clapper, director of the Defense Intelligence Agency, told a recent congressional hearing.

“We’re looking at a future in which every major power has nuclear weapons,” agreed Michael Vlahos, a strategist at the Center for Naval Analyses. “The only question is whether they use them or not.”

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Most analysts believe that they already know the answer to that question.

“Somewhere, some time--but in this decade--somebody . . . is going to set off a nuclear weapon in deadly earnest,” said Rear Adm. Edward D. Shaefer Jr., director of naval intelligence.

Not everyone agrees with Shaefer’s prediction. A few political scientists, such as UC Berkeley’s Kenneth Waltz, even argue that proliferation can make the world more stable in the long run by making war so dangerous that it is unthinkable.

But nearly everyone agrees that as more countries acquire nuclear weapons, chances of something going wrong--a misguided war, a miscalculation in crisis or a simple accident--will increase.

That new reality has prompted a basic change in U.S. policy.

Once, the United States concentrated on preventing countries from gaining nuclear technology. Now, U.S. policy acknowledges that more countries may acquire atomic weapons and has added two additional goals: making proliferation safer and building “counter-proliferation” weapons in case a U.S. President decides to destroy a budding arsenal.

For more than a decade, for example, the United States cut off military sales to Pakistan to discourage it from pursuing nuclear weapons. But now that Pakistan’s bomb is virtually acknowledged, the Clinton Administration is proposing to relax the sanctions and to begin talks on how to prevent accidental nuclear war.

Benjamin Frankel, editor of the journal Security Studies, calls this the “New York City public school solution”: Like teen-agers and sex, nations that want nuclear weapons are going to do it anyway, and the best we can do is to help them do it safely.

At the same time, the Pentagon has launched a new counter-proliferation program to develop forces capable of destroying nuclear weapons and facilities abroad--to prevent their shipment to another country or their use in a local war.

But proliferation does not only increase the probability of nuclear wars. It also changes the balance of world power and diminishes the superpower status of the United States. In the Gulf War, U.S. strategists worried that Iraq might use chemical weapons against U.S. troops or Israeli civilians--but they never had to worry about nuclear weapons. If the United States ever considers another war with Iran, Iraq or North Korea, the story could be different.

“This is going to put us in a world much like that of the 1930s: a world of several equally sophisticated military powers, with no one clearly on top,” Vlahos warned. “The conventional wisdom in defense planning is that we dominate the ‘battle space’ and we always will. But it isn’t necessarily so. Nuclear weapons are a great equalizer.”

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And that has a political as well as military impact. If a potential adversary has nuclear weapons, “the cost of intervention for the United States is much higher,” a senior U.S. official said. This means that the other country has less reason to fear the United States--and a freer hand to intimidate its own neighbors.

The proliferation outlook, region by region:

* North Korea: CIA chief R. James Woolsey says the Communist regime of Kim Il Sung probably already has made at least one nuclear weapon using plutonium from its own atomic power plants. If North Korea goes ahead with plans to remove the fuel from its 25-megawatt reactor at Yongbyon, it could extract enough plutonium to build several more. Coupled with a determined program to develop ballistic missiles--and a penchant for selling weaponry to such customers as Iran and Syria--the North Korean nuclear project is the world’s most dangerous military enterprise.

If North Korea goes nuclear, the effect on the rest of Asia will be immediate. South Korea, which abandoned nuclear weapons research under U.S. pressure in the 1970s, would clamor for atomic weapons. Japan, which officially has renounced nuclear weapons, would reconsider that stand--and U.S. experts believe that Tokyo could build a bomb within months. Last year, Japan briefly balked at endorsing an indefinite extension of the Nuclear Non-Proliferation Treaty--apparently because some officials were not sure they could promise to stay non-nuclear forever.

Next door, China is already modernizing its nuclear force, testing more accurate warheads and better missiles for medium-range targets such as Taiwan or Japan and for long-range targets such as the United States and European Russia.

A North Korean nuclear threat could prompt China to add more weapons to its arsenal of at least 450 warheads. China’s nuclear strength, in turn, worries two neighbors: India, which already has nuclear warheads on medium-range ballistic missiles, and Taiwan, which has twice been stopped by the United States from launching a nuclear program.

* Iran and Iraq: The CIA says that Saddam Hussein’s Iraq was only a year or two from testing a nuclear weapon when the Gulf War interrupted his program. U.S. officials say they believe that Iraq’s weapon development program is moribund but almost certainly will be revived if U.N. inspections ease up.

Meanwhile, Iran is working hard to acquire nuclear weapons. The CIA has said Tehran’s dogged domestic research program is making only slow progress and still appears at least eight years from producing a weapon. As a result, Iran has stepped up its efforts to buy warheads or nuclear material from the former Soviet Union. Iranian agents reportedly have been sighted in Russia and Kazakhstan in search of a deal.

The impact of an Iranian bomb would be immense--in both the Middle East and farther afield. Nuclear weapons would make Iran the most powerful country on the gulf, able to intimidate its neighbors without fear of military reaction from the United States or Iraq. A nuclear Iran could seize territory or demand cuts in others’ oil production. Saudi Arabia, Iraq and Israel would all view an Iranian bomb as a direct threat.

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The Saudis would probably react by seeking more protection from the United States. Israeli leaders might well be tempted to launch a preemptive strike against the Iranian nuclear force, just as they bombed Iraq’s Osirak reactor in 1981. Even Turkey, Kazakhstan and Russia would feel nervous about an Iranian bomb.

* Libya: Col. Moammar Kadafi reportedly has been negotiating to buy ballistic missiles from North Korea and may also be in the market for nuclear weapons. U.S. analysts do not believe that Libya has significant nuclear research ability of its own. If Libya acquired nuclear weapons, its potential targets would include Israel, Egypt and U.S. forces in Europe. And Libya’s long history of support for terrorist groups, from Palestinian guerrillas to the Irish Republican Army, would raise the specter of an atomic weapon falling into their hands.

* Ukraine: In January, Ukrainian President Leonid Kravchuk signed agreements with the United States and Russia to remove and dismantle the estimated 1,656 nuclear warheads in Ukraine within seven years. But U.S. officials still worry privately that Ukraine, fearful of neighboring Russia, will be tempted to hang on to a deterrent force.

“We’re holding our breath and crossing our fingers,” one official admitted.

A Ukrainian nuclear force would heighten tension in Eastern Europe--and probably prompt neighboring Germany, Poland, Hungary and Belarus to reconsider their non-nuclear status. And in the event of a civil war in Ukraine, the presence of nuclear weapons could provoke Russian intervention rather than deter it.

The ability of smaller countries to acquire nuclear weapons does not mean that they will actually do so, officials noted.

In fact, the last decade offers three examples of countries that abandoned nuclear weapons projects. South Africa built a nuclear force of six bombs, apparently for possible use against its black citizens, but destroyed them in 1993. Brazil and Argentina were on the way to building nuclear arsenals for use against each other but managed to turn back in 1991.

Instead, the lesson of half a century of nuclear weaponry is that the drive to acquire atomic hardware is rarely predictable.

Josef Stalin shocked the United States when he detonated the first Soviet atom bomb in 1949; China surprised the West in 1964; Iraq stunned the United Nations when its nuclear enterprise was discovered in 1992.

“The bottom line is that we’ve seen so many sudden and surprising developments that we have to anticipate more of them,” said Leonard S. Spector, a non-proliferation specialist at the Carnegie Endowment for International Peace.

“For example, the nuclear allergy in Ukraine and Japan . . . may not last forever,” he said. “As soon as the security environment becomes more dangerous, people begin to rethink things.

“The danger is to think that there is only going to be incremental change. That isn’t going to happen. There are probably going to be some big shocks.”

Nuclear Weapons: A Growth Industry

Countries ranging from Israel to Pakistan have developed atomic weapons, thanks to the spread of technology around the globe. Many more are on the verge of having weapons, either through their own development programs or by buying necessary components.

COUNTRIES WITH NUCLEAR WEAPONS:

United States, Russia, China, Britain, France, Israel, India, Pakistan, Ukraine*, Belarus*, Kazakhstan*

* Ukraine, Belarus and Kazakhstan inherited part of the nuclear forces of the former Soviet Union; all three have pledged to remove or dismantle nuclear warheads on their territory.

ON THE NUCLEAR THRESHOLD:

North Korea

COUNTRIES WITH ACTIVE DEVELOPMENT PROGRAMS:

Iraq, Iran

COUNTRIES WITH POTENTIAL FOR NUCLEAR WEAPONS:

Algeria, Libya, Egypt, South Korea, Japan, Taiwan, Poland, Germany

WHAT TO WATCH

1. North Korea’s nuclear project is the world’s most dangerous military enterprise.

2. Iraq was only a year or two from testing a nuclear weapon when the Persian Gulf interrupted, the CIA says.

3. If Libya acquires nuclear weapons, potential targets would include Israel and Egypt.

4. A Ukrainian nuclear force would heighten tension in East Europe--and probably prompt neighboring Germany, Hungary and Poland to speed up development of nuclear weapons.