National Agenda : When the Lights Go Out at the Kremlin : * There are several scenarios, none good, for the former union.

It was James A. Baker III, the U.S. secretary of state, who gave voice to the nightmare scenario that, as of this week, seems suddenly and horrifyingly plausible.

The former Union of Soviet Socialist Republics has reached critical mass, Baker warned. And what may result is something like the present-day ethnic warfare in Yugoslavia--with thousands of nuclear weapons tossed in for good measure.

Allow his country to break up along ethnic fault lines, Soviet President Mikhail S. Gorbachev cautioned, and the Yugoslav conflict will look like a “simple joke” in comparison.

Such dire, Cassandra-like predictions won immediate converts both here and in the West. For months now, Russians have uneasily watched TV reports of the killings and brutal military operations in Yugoslavia--whose name means “the land of the southern Slavs”--feeling that they might be witnessing a dress rehearsal for their own country’s apocalyptic future.

For more than three years, Gorbachev and his team, some of the brightest minds in the Soviet Union, struggled and ultimately failed to resolve the murderous feud waged by the Armenians and the Azeris, two neighboring Transcaucasian peoples.

“It will always be with us,” a despondent executive of the official Tass news agency once confided. “It has become our Ulster.”

But since then, other “Ulsters” have flared across the former Soviet Union in out-of-the-way places with exotic, little-known names like Osh or Ossetia. And all this has happened when there is still an armature of centralized power, a unified Soviet armed forces and a Ministry of the Interior. What will happen when all this vanishes?

“One cannot be too alarmist about this,” Simon Lunn, the deputy secretary general of the North Atlantic Assembly, told the Reuters news agency Monday in Brussels. “No one in the West or in the Soviet Union seems to know how to prevent this free fall.”

The old Cold War standoff, based on nuclear strategy known as “MAD”--Mutual Assured Destruction--never seemed more stable or attractive than it does now. A few days ago, a senior U.S. government specialist on the Soviet Union, musing out loud over a plateful of smoked fish at a dimly lit Soviet restaurant, said American officials, by and large, had badly erred in overestimating the Soviet system’s capacity for reform.

Once political and economic change became irreversible, the gigantic country itself, the result of centuries of relentless expansion by the Russian center, began to collapse upon itself, the specialist said.

Optimistic ideas of a “reformed Soviet Union,” he said, were nothing but a paradox. The country, historically speaking, existed due to tyranny and terror. Change doomed it.

Such, too, is now the argument of embittered Soviet conservatives. For them, the accord reached last weekend by Russian President Boris N. Yeltsin with the leaders of Ukraine and Belarus, dissolving the Soviet Union in favor of a “Commonwealth of Independent States,” is a reversal of centuries of centralization and consolidation that will unleash vastly destructive forces.

“One thing can be said with certainty now--a lot of explosives have been planted under the country’s foundation. . . . To mention just one thing, a chasm has been opened between the Slavic and the Muslim republics,” Sergei N. Baburin, the leader of the conservative faction in the Soviet national legislature, commented. “This split is going to play a highly damaging, downright murderous role in the near future.

“Another thing--the very idea of a federative state, with a tight alliance between its constituent parts, has now been destroyed,” Baburin said. “We can now talk about the final dismantling of the Soviet Union as an entity under international law. This is an entirely new historical reality.”

Keenly conscious of the historical parallels with Yugoslavia, a country that only appeared on the map of Europe after World War I, the advocates of a radical realignment of power assert that it was the Soviet Union, and the Russian empire that antedated it, that was the artificial “historical reality.”

The source of the instability, they maintain, comes from trying to prolong an unnatural creation.

“For the world community, a civilized community of free states which guarantee peace and human rights must take the place of the irresponsible union,” the Russian foreign minister, Andrei V. Kozyrev, told the German newspaper Bild Zeitung.

For Yeltsin, Ukrainian President Leonid M. Kravchuk and Belarus Parliament chairman Stanislav Shushkevich, scrapping the centralized machinery of the Soviet Union and granting the republics genuine independence is the only way left out of the country’s multifaceted crisis.

“We are extremely concerned over the situation resulting from the disintegration of the union,” Shushkevich told Tass. “Because of this, and acting within the framework of rights granted to us by the Constitution, we came up with the initiative to sign the agreement on the establishment of a commonwealth of the three independent states.”

It seems like the revenge of history over the Marxist-Leninist doctrine that had been official cant here for more than seven decades. Marxism denied the importance of nationalism, terming it antithetical to class interests. Nationalism, therefore, could not exist in a socialist Soviet Union.

The refutation of this dogma has been as sudden as the “winds of change” British Prime Minister Harold Macmillan correctly predicted would sweep away the old colonial empires in Africa. For instance, the Ukrainians, told for at least a century that they were really “Little Russians,” voted themselves out of the Soviet Union at the beginning of this month.

By all appearances, that single act sounded the death knell for the land both Peter the Great and V.I. Lenin built. “Farewell empire!” read one banner carried down Kiev’s main street. Not only were the Ukrainians leaving it, they were killing it off.

“Independence has been gained by half of Soviet sugar, one-third of Soviet steel, one-fourth of coal and corn, and almost every fifth citizen,” Russian television commented. That mass exodus of resources and human talents meant Gorbachev’s project for a new political union with a slimmed down central government no longer satisfied the demands of Ukrainians, Russians and others.

As an additional stabilizing factor, in creating their commonwealth, the Slavic trio have made it clear from the start that they are not forming the equivalent of a Soviet club for the rich. The commonwealth-- sodruzhestvo --is open to all, they said, the Kremlin’s former Warsaw Pact allies included.

“I believe that the Armenians and some others will come along,” Kozyrev said in his interview with Bild Zeitung. “The federation also remains open for the former East Bloc states, for example, for Bulgaria and Romania.”

To reassure Secretary Baker and the rest of the world that the spectacular easing of military tensions in the world achieved under Gorbachev will continue, the Slavic leaders have said they will form a single body to exercise command over the Soviet nuclear arsenal and the “common military-strategic space.”

“Creation of a commonwealth of independent states is the right of their governments,” said an approving Valeriu Muravschy, prime minister of the republic of Moldova. “The major argument in favor of their decision was the necessity to assert control over nuclear weapons, which worries the West the most.”

A world worried about a potential repeat of what Soviets call the “Yugoslav variant,” albeit on an immeasurably vaster scale, also needs to look closely at which peoples will be a part of the Yeltsin-engineered commonwealth. If it is only the three original signatories of the commonwealth agreement, it will already embrace 73% of the Soviet Union’s population and 80% of its land area.

What’s more, Russians, Ukrainians and Belarussians are not, like Serbs and Croats, embittered by feuds that date to World War II atrocities and beyond. They share the same Slavic blood, vocabulary and customs. In fact, there is a joke that there are only two kinds of Soviet soup: Russian shchi , made of cabbages and beets, and Ukrainian borscht , made of beets and cabbages.

Under past Kremlin rulers, nuclear weapons were intentionally concentrated in the Slavic heartland and a fourth republic, Kazakhstan, which has a large Russian and Ukrainian population. Despite decades of rhetoric about the equality of all peoples under socialism, the Soviet Strategic Rocket Forces who man the country’s ICBM bases are made up almost totally of Slavs.

Russia, Ukraine and Belarus even agreed explicitly at their talks to recognize each other’s present-day borders and territorial integrity, another crucial step to minimizing potential sources of friction. In particular, Ukraine has been frightened that Russia might one day lay claim to its northern border regions or the Crimea.

“The decision (on the commonwealth) has a lot of weak points,” Oleg G. Rumyantsev, secretary of the Russian parliamentary committee writing a new Russian constitution, said. “But one point outweighing them all is the nonaggression pact, which is really of paramount importance at this stage.”

In Lunn’s opinion, even if the Slavic republics have formally agreed to work together, conflicts are likely, for example, over how to slice up the economic pie or assure command over nuclear weapons or units of the Soviet armed forces based on their territories.

But there is little debate that the chief potential source for large-scale ethnic conflict would be the uneasy interface between the European, Slavic world and the Muslim and Asian East. The uniform red in which maps of the Soviet Union were long tinted by the West served to camouflage the fact that these were starkly different lands.

“I have never understood what the Muslims want, so don’t ask me,” Anatoly N. Medvedev, a centrist member of the Soviet legislature, commented Monday. “But we can’t conceivably want to kill each other, so why not come to terms, all of us?”

In Central Asia, Gorbachev’s reforms made possible a renaissance both of Islam and the shameless, calculated conversion of local Communist leaders to the flag-waving nationalist cause. This religious and patriotic fervor could be channeled in the future to mobilize the masses against Moscow or the “infidels” from the northwest.

For instance, Islam A. Karimov, the former leader of the Uzbekistan Communist Party, supposedly told a crowd of 20,000 people in the city of Namangan on Monday that he is really a Muslim, and that an “Islamic state” would be created step by step. Now running for the presidency of Uzbekistan, Karimov must contend with a surge in local religious fervor.

Sheer economics, however, may keep these underdeveloped, sometimes poverty-stricken lands in the Slavic orbit, and many Europeans think they will have little alternative. The quality of Uzbekistan’s huge annual cotton crop, for example, is too poor to be sold on the world market, so it goes to the European Soviet Union.

Mountainous Tadzhikistan, where only 7% of the soil can be tilled, may join Yeltsin’s commonwealth out of economic necessity, according to press reports from the capital, Dushanbe. But there was also talk there on Monday of rapidly forming a rival, Muslim-dominated geopolitical bloc--”the Commonwealth of Sovereign States of Central Asia.”

Looking askance at the Communist Party pedigree of most of Central Asia’s crop of ruling nationalists, reformers accuse them of embracing independence as a way to safeguard their own power.

Svyatoslav Fyodorov, an eye surgeon and one of his country’s best-known entrepreneurs, said the collapse of the Soviet Union can lead to nothing but the “creation of 15 separate concentration camps” as each republic sets up barriers to protect its sovereignty from the world at large.

The common people will gain nothing from all this, he asserted. On the other hand, “senior executives have become independent from Gorbachev and Yeltsin.” The parade of independence declarations has been profitable for them.

If there is instability in and around the new commonwealth, it seems fated to be the sort of low-intensity regional warfare, terrorism and violence that has flared here and there in the Soviet Union since at least February, 1988, when the Armenia-Azerbaijan quarrel over the Nagorno-Karabakh territory began escalating.

Where Trouble Looms The determination of former republics to never again be dominated by “the center”--whether Moscow or Minsk--is just one of the powerful forces at work as efforts continue to fashion some new order out of chaos in what was the Soviet Union.

Another is the long-suppressed antagonism that many national groups within the former Soviet Union feel toward each other. Among the more dangerous potential hot spots: 1 Moldova--Disputes rage between independence-minded Moldovans and both the Russian and Gagauz minorities who want to set their own course.

2 Russia--A number of minorities within the Russian Federation demand total independence, with particularly militant movements in the largely Muslim Chechen-Ingush region and in Tatarstan. 3 Georgia--Three minority groups, Ossetians, Abkhazians and Meskhetian Turks, all have serious arguments with the Georgian majority over territorial issues and relations with Moscow.

4 Azerbaijan--There has already been open warfare between Azeris and Armenians for nearly four years over the disputed territory of Nagorno-Karabakh.

5 Uzbekistan--In addition to a border dispute with neighboring Tadzhikistan, minority Meskhetian Turks are in conflict over alleged job and land discrimination.

6 Kyrgyzstan--A longstanding land controversy between Kirghiz and Uzbeks has flared periodically into violence.