KIZIL, U.S.S.R. -- Every week, hundreds of ethnic Russian families in this remote region along the Mongolian border pack their belongings and join an exodus north, across the Sayan mountain range that separates the autonomous republic of Tuva from Russia proper.

Russian settlers first reached the once feudal state of Tuva in the late 19th century. Tens of thousands more came this century, colonizing the barren plains and inhospitable mountains and bringing Slavic civilization to the indigenous nomadic, Mongoloid people who live in this geographical center of Asia.

Now the Russians are beginning to go home, reversing six centuries of steady expansion. They are fleeing the Soviet Union's latest outburst of ethnic turmoil.

"Some Russians are leaving because of the lack of economic opportunities. But others are leaving because they are afraid, for themselves and for their children," said Altai Piche-Ool, a Tuvinian deputy in the Russian legislature, describing a dramatic increase in anti-Russian incidents in this autonomous republic of 300,000 people over the last year.

A similar trend of Russian emigration can be observed all around the fringes of what was once the Russian empire -- from the Baltic republics to Azerbaijan in the Transcaucasus to Tajikistan and Kirghizia in Central Asia. With the collapse of Communist ideology as an integrating force, the Soviet Union is breaking down into the separate nations that populate the vast Eurasian landmass.

Over the last year, many Russians have begun to face the thought that the Soviet Union might fall apart. President Mikhail Gorbachev spoke last month of the possibility of the world's second superpower disintegrating into "15 nuclear states." He aims to keep this from happening by persuading the republics to cede some of their sovereignty -- over defense and foreign policy, for example -- to the central government under a new union treaty.

In a manifesto published in the Soviet press, exiled Russian writer Alexander Solzhenitsyn called for the peaceful secession of the Baltic, Central Asian and Transcaucasian republics. He suggested that the traditional Slavic heartland of Russia, the Ukraine and Byelorussia, plus Russian-populated parts of Kazakhstan, form a "Russian Union." "We have to make a decisive choice: between the empire which is destroying us and the moral and physical survival of our nation," declared the Nobel Prize laureate.

Many Russian politicians and intellectuals appear to share Solzhenitsyn's belief that the Soviet Union in its present form is doomed. The main political divide here is not over whether to preserve the centralized Soviet state built by Vladimir Lenin and Joseph Stalin, but how to ensure a peaceful transition to a looser confederation of sovereign republics. There is a widespread feeling that, at the very least, the three Baltic states will go their own way.

If the Soviet Union were an empire in the traditional sense, the process of decolonization might be relatively clear-cut. In fact, it is the product of many centuries of Russian expansion culminating in revolution, civil war and a blood-soaked attempt to build the world's first socialist society.

In the process, colonizers and colonized became hopelessly mixed up. All Soviet citizens, Russians and non-Russians alike, have legitimate historical grievances.

The present administrative boundaries of the Soviet Union are almost arbitrary, reflecting neither historic nor demographic reality. One out of every four Soviet citizens -- including about 24 million ethnic Russians -- live outside their titular republic. Any attempt to unscramble this multinational community into individual nation states could provoke uncontrollable ethnic violence.

Ethnic disturbances have already created a huge and growing refugee problem. According to official estimates, there are now nearly 750,000 refugees in the Soviet Union, half of them Russians. Uprooted from their homes, frequently unemployed and living in appalling conditions, the refugees are easy prey for political demagogues. The anti-Armenian and anti-Russian pogroms that took place in Azerbaijan last January were largely the work of Azerbaijani refugees from Armenia.

"It's quite easy to imagine a chain reaction," said Viktor Rezunenko, who was forced to flee the Azerbaijani capital, Baku, and now heads a Russian refugee center in Moscow. "Many refugees have lost faith and patience. There are some who might resort to the same violence against people they consider foreigners in Russia as was used against us in Azerbaijan. The situation is quite unpredictable."

The Russian exodus from Tuva began late last year, following an alarming rise in the crime rate that affected Russians and Tuvinians alike. But it has quickened over the last few months as relations between the two communities have deteriorated. Leaflets with slogans like "Go back to Russia, otherwise you'll pay" have begun to appear in the streets of Kizil, the capital. Gangs of Tuvinian youths have roamed through remote villages, setting Russian homes on fire, smashing windows and stoning cars.

In one recent incident, reported in the central Soviet press, a young Russian was murdered in Kizil after failing to reply in Tuvinian to the question, "Do you have a smoke?" At about the same time, two Russian fishermen and a 14-year-old boy were murdered near a lake, their bodies charred in an attempt to prevent recognition.

"As soon as I can find another job back in Russia, I will leave as well," said Oleg, a Russian collective farm worker who did not want to give his last name. "Why stick around? I fear they could start taking our children hostage."

About 2,700 Russians over age 16 are officially reported to have left Tuva over the last two months, compared to 6,000 for all of last year. The departing Russians include many doctors and skilled technicians whose presence is vital for the Tuvinian economy. There is already talk of closing local factories, including a major asbestos plant, because of a shortage of trained experts.

Tuva was the last chunk of Asia to be absorbed into the Soviet Union, becoming an autonomous republic within the Russian federation in 1944. Bordering on Mongolia, it marks the outward limit of Russia's territorial expansion.

The Russian march to the east began in the 15th century after the defeat of the Mongolian Golden Horde by czar Ivan the Terrible. Siberia was colonized in the 16th and 17th centuries. Russian armies reached the borders of Afghanistan in the 19th century, alarming the British who felt that their hold over India was threatened.

Educated Tuvinians concede that the Russian colonization of their country had many positive aspects. The Russian immigrants introduced European culture, technology, clothes, even bathrooms to a formerly nomadic people. But they also undermined the Buddhist religion, the respect of the young for the old and the Tuvinian language. Tuvinians say that the curse of alcoholism dates from the Soviet period.

"The Russians raised our living standards, but they destroyed our traditions," said Vyacheslav Solchak, a commentator for Kizil television and an ethnic Tuvinian. "They said there was just one nationality, the Soviet nationality. They forgot that we had our own culture and language. My boy is 7 years old, but he does not speak Tuvinian. That is my great misfortune."

At the Kizil coffee bar in the center of this typical Soviet provincial town, the rival ethnic groups eye each other warily from separate tables. The tension jumps appreciably when a group of Russian Special Forces or spetznaz troops, flown to Tuva to keep order, swagger into the restaurant, swinging their nightsticks.

"If a Russian picks a fight with us, the spetznaz will always take it out on us. They always assume that we start the trouble," hissed a Tuvinian student, who asked not to be named. "The Russians take everything we have: our forests, our gold, our temples, even our asbestos."

It is possible to sense a different kind of anger -- a quiet, burning frustration -- at the Russian refugee center in Moscow, just behind Red Square.

Russians forced to leave the outlying republics because of ethnic violence crowd into the center in search of jobs and places to stay. Frequently they are told that there is nothing for them in Moscow and they will have to move somewhere else.

"We believed in the slogan of friendship between peoples. We did our internationalist duty for 32 years," said Nikolai Trubavin, a Russian oil worker who fled the Central Asian republic of Tajikistan earlier this year after ethnic riots. "Now we find ourselves without a home and without a homeland. Nobody seems to want us."

Some conservatives accuse Gorbachev of irresponsibly frittering away the gains of a millennium of Russian expansion.

In a recent interview, nationalist writer Alexander Prokhonov described the disintegration of the Soviet Union as "a horrifying misfortune, unacceptable to the Russian mind."

He predicted that the continued unraveling of the empire could lead to civil war.

Although he claims to speak for sections of the military as well as conservatives in the Communist Party, Prokhonov seems to be in a minority. A more common reaction, even among avowed Russian nationalists, is that Mother Russia may be better off without the non-Russian republics that have been taking advantage of her for far too long.

"Most of these countries asked to become part of Russia in the first place. We have treated them as our guests," said Ilya Glazunov, a Russian painter attracted by nationalist themes. "If a guest does not want to stay in my house, he has a perfect right to leave. But he should not think I will let him take my candleholders along with him."

Even if Russia was reduced to the Slavic heartland envisaged by Solzhenitsyn, it would still be the world's largest country, geographically. The combined population of Russia, the Ukraine and Byelorussia is 210 million people. Together, these three republics produce more than 92 percent of the Soviet Union's oil and gas, 80 percent of its industrial output and about 80 percent of its food.

Opposition to Baltic independence has come mainly from Russians living in the Baltic states who fear that they could become second-class citizens in the event of secession. It is these so-called "aliens" -- people living outside their own republics -- who constitute the most powerful social and political force for the preservation of the Soviet Union in its present form.

As the Baltic states press ahead with their plans for independence, conservative journals such as Literaturnaya Rossiya have been running articles suggesting that Russia will be better off without them. The argument is based on the fact that Russian raw materials are sold at grossly subsidized prices to the non-Russian republics. In return, Russia is obliged to buy expensive finished products from the republics at above world prices.

The "patriots" do express worries about the fate of the nearly 2 million Russians living in the Baltic republics. But their main concern is the future of Russia as a strong, centralized state.

In a recent article for Literaturnaya Rossiya, commentator Eduard Volodin called for the return of Russian soldiers and officers to Russia. Describing the Russian officer corps as "the gold reserve of our country," he said it risks becoming bogged down in irresolvable local conflicts. "When we stand at the edge of national catastrophe, we cannot continue to take part in the ambitious games of outlying nationalist groups, allowing our army to rot.

"Russia will be alone, but this does not mean that it will become a second-rate state, left out of the orchestra of world politics. Russia still controls the Eurasian continent, with all its raw materials and industrial potential, intellectual power, nuclear missiles and modern army. All this taken together will still leave us among the leading powers," said Volodin.

At the other end of the political spectrum, the progressives openly support the national aspirations of the Baltic states, but draw the line at the defection of the Ukraine and Byelorussia.

"It's in my own interests for Lithuania to become independent," said Alexander Ogorodnikov of the newly formed Christian Democratic Union. "If both Lithuania and Russia were free, we would be able to sell our oil for real currency, not just bits of paper. I cannot think of this empire as a Russian empire, my empire. It is the empire of an alien ideology, Marxism."