While the Bush administration is preoccupied with the unanticipated crisis in the Persian Gulf, another challenge to U.S. national security is looming on the horizon: the danger that the world will be confronted with the unprecedented specter of a nuclear superpower sliding into bloody chaos.

The disorderly disintegration of the Soviet state is not yet inevitable -- few historic events are until they actually take place. But the prospect is real and frightening enough to warrant President Bush's taking the time to review his policy of conducting business as usual with a central government in Moscow that is becoming progressively divorced from the rest of the country.

Americans traditionally do not like to think about the possibility of a friendly foreign leader like Mikhail S. Gorbachev being ousted by his disgruntled people. Still there is no escape from the fact that all his contributions to international peace and freedom notwithstanding, to his own population -- tired of economic deprivation, lawlessness and ethnic unrest -- he looks little better than the shah did to the Iranians or Anwar Sadat to the Egyptians.

Also the notion of anarchy and, perhaps, of civil war in a nation such as the Soviet Union -- with its nuclear arms and power stations and its chemical weapons depots -- contradicts elementary logic. Optimists both inside and outside the U.S.S.R. point out that nobody would benefit from such an advanced and well-armed state disintegrating into civil war. But by that criteria of rationality, most major wars (certainly not World War I) would never have taken place. The numerous ethnic grievances coming on top of economic deprivation fuel powerful nationalist passions in many parts of the Soviet Union. And local leaders in these volatile parts play more and more frequently by Beirut's rules -- ruthlessly promoting the parochial interests of their own constituencies without regard to the common good. Under the circumstances, it was perfectly fitting for Gorbachev to warn about the growing phenomenon of Lebanization of the Soviet Union -- a phenomenon that is already beginning to affect the army and the KGB.

The absence of a feeling of common destiny in moments of trial reflects a centuries-honored tradition and actually predates the transformation of Russia into a multinational empire. As the great Russian prerevolutionary historian Vasily Klyuchevsky wrote about the "Time of Troubles" back in the 17th century: "vis-a`-vis the state, the people of Moscovy behaved as displeased servants or tenants rather than disobedient citizens. They ... developed a unique form of political protest: individuals who could not coexist with the existing order would not revolt against it, but rather left it by running away from the country."

Rejecting the notion of common destiny is exactly what the republics, provinces and even the cities are trying to do today. National aspirations do not tell the whole story behind the centrifugal tendencies in the Soviet Union. They cannot explain the resolution of the Odessa City Council that expressed the preference of this major Russian/Ukranian port city on the Black Sea for sovereign status modeled after Singapore's. And they have nothing to do with the independence movement in the Russian Far East and the desire there to secede from the rest of the Soviet Union.

However, the peoples of the Soviet Union cannot simply run away from each other. Borders between the U.S.S.R.'s republics are no less arbitrary than those of colonial Africa. Sixty million Soviet citizens live outside their own ethnic areas. Smaller republics may secede with a tolerable level of pain. But any Ukrainian or Byelorussian attempt to establish independence would, in all likelihood, trigger a great deal of violence and perhaps lead to civil war. The combination of an increase in radical nationalist sentiments in these two Slavic republics and a growing popular contempt for Gorbachev's leadership -- which is not bold enough to lead the change and not brutal enough to arrest it -- puts Ukrainian and Byelorussian secession on the Soviet national agenda for the first time since the Bolsheviks consolidated their power 70 years ago.

Americans should not be blinded by the fact that unrest in the Soviet Union lacks two clearly-defined sides like the North and South in the Civil War in the United States. Both the Time of Troubles and, more recently, the Russian revolution in 1917 have been increasingly mentioned by Soviet commentators of all stripes as relevant to their nation's current predicament. These followed a pattern of: (1) disintegration of the central authority, (2) dismemberment of the state into hostile components followed by (3) a prolonged process of crystallization into principal parties, one of which eventually prevailed.

In this tragic pattern bound to be repeated? Gorbachev's performance gives few grounds for optimism. Like the ill-fated provisional government of Prime Minister Alexander F. Kerensky in 1917, the Soviet president is accruing ever-expanding formal powers, but these only serve to camouflage his declining authority. Like Kerensky, Gorbachev pursues the illusion of national consolidation in a bitterly divided nation, when the only solution is contingent on making painful choices that could possibly exacerbate the divisions.

What may save the Soviet Union is that the Soviet republics, while asserting their sovereignty, are prepared to enter mutually beneficial arrangements. That is exactly what the Russian parliament chairman, Boris N. Yeltsin, is counting on in his effort to create a new voluntary community of sovereign but interdependent states on Soviet territory.

Yeltsin's effort represents the best hope of averting explosive anarchy in the U.S.S.R., and it deserves U.S. support. Of course, as long as Gorbachev remains the leader, the United States has to deal with him and must avoid -- as much as possible -- undermining his position. But relations with the Soviet president should be balanced by developing contacts with the new powers in the Soviet Union -- most notably the government of Russia, which is dominated by radical reformers.

This government enjoys much greater credibility at home than Gorbachev's team does. How long this credibility will last -- in the context of the emerging economic disaster -- is impossible to predict. But it is surely in the U.S. national interest to find a formula to offer Yeltsin's government a helping hand in order to keep the Soviet Union from falling into the abyss.

The writer is a senior associate at the Carnegie Endowment for International Peace.