FERGANA, U.S.S.R. -- Conquered by czarist generals just over a century ago during Russia's great march eastward, this fertile valley in the heart of Central Asia offers a grim vision of how the Soviet Union's "internal empire" could one day break up.

"The valley was like a volcano waiting to go off," said Baktier Mamadiev, a local Communist Party activist, describing the explosive mix of ethnic rivalry, environmental catastrophe, economic crisis and overpopulation that has cost the lives of about 500 people in the region over the last two years.

The Fergana valley first hit the headlines in June 1989 with the massacre of Meskhetian Turks, a tiny nation exiled to Central Asia by Joseph Stalin because he suspected them of disloyalty in World War II. Bands of Uzbek youths roamed the valley, looting and burning Turkish homes and laying siege to Communist Party buildings. About 100 Turks were killed.

A year later, even more horrifying ethnic violence erupted at the eastern end of the valley, in the Kirghizian town of Osh. This time, it was the Uzbeks who suffered most of the casualties as the result of a land dispute with Kirghiz that cost more than 300 lives, according to official estimates.

To outward appearances, all is again calm. Russian and Uzbek, Turk and Jew, Kirghiz and Tatar rub shoulders in the bazaars and teahouses. The curfew has been relaxed. It is almost as if the frenzy of killings of the last two summers never took place.

After a few moments' conversation, however, the peaceful facade breaks down. Uzbeks start talking about the harm done to their land by the Russian "colonizers." Russians complain about a lack of physical security and new policies under which the best jobs go to local people.

Before the violence began, the natural blessings of the valley -- a 200-mile-long plain surrounded by mountains and irrigated by snow-fed streams and rivers -- attracted immigrants from all over the Soviet Union. The climate -- hot summers, mild winters -- is benevolent. Virtually anything will grow in the rich soil. Longtime residents claim that the air here was sweeter than anywhere else in Central Asia.

That was before the central planners in Moscow ordered the construction of giant chemical factories and fertilizer plants in the valley and turned over most of the agricultural land to the production of cotton. Uzbek nationalists now curse the factories that pump untreated effluent into the air and blame the cotton monoculture for the region's endemic poverty and backwardness.

But the social problems and flareups in ethnic violence seem secondary to the most startling trend of all: The Russians are going home.

"If we could find apartments back in Russia, most of us would be on the first plane out," said Natasha Khatuntsev, who holds the title of champion cyclist of Uzbekistan. "Under the new language law, they are telling us all to learn Uzbek. But how do you learn a new language when you are over 50? We are beginning to understand that there is no future for us here."

Across town, a group of Uzbek intellectuals sat cross-legged on a rug-covered floor, eating grapes and discussing the evils of "Russian colonialism." "Russians are lazy," complained one of the guests, a university professor. "We Uzbeks are willing to build our own houses, work on the land. The Russians wait until the state provides them with apartments. That's why they came here: so that we would be their slaves."

The term "decolonialization" is offensive to Soviet officials. But it is probably the best one-word description of the painful political process now getting underway in places like the Fergana valley.

"England has given up its colonies. France has given up its colonies. Even America doesn't have colonies. This is where Gorbachev's policy is leading. It's the only sensible policy," said Shukrulla Yusupov, a leading Uzbek writer who spent four years in a Stalinist labor camp in the early 1950s but is now a member of the republic's presidential council.

Osh, where last summer's violence began, is still closed to Western reporters. The scale of the atrocities was reflected in an eyewitness report from a Russian journalist, Yuri Rost, who described "people whose throats were slashed and their blood drained (as they do when they slaughter sheep); people killed and then burned to cinders; noses and ears cut off and eyes plucked out; a human head on a pole; women raped by dozens of animals and subsequently killed."

"It took us 30 years to build all this and it was destroyed in 30 minutes," said Alikhan Vezirov, a Meskhetian electrical engineer, inspecting the ruins of his burned-out home in Kokand, at the western end of the valley. "Things may seem peaceful enough now but, after everything we've been through, we're not going to risk waiting around for the final destruction of our nation."

Vezirov was one of about 35,000 Meskhetian Turks airlifted to European Russia when ethnic violence first erupted in the Fergana valley in 1989. He recently returned to Kokand to sell his seven-room villa to an Uzbek for what he says was a ludicrously low price.

Just why the Meskhetians were singled out remains somewhat perplexing. Uzbeks have much more in common with Meshkhetians -- notably their Moslem faith and Turkish origins -- than they do with Russians. One theory is that the very insignificance of the Meskhetian minority made them an easy target. Unlike the much more numerous Russian community, most of whom live in relatively secure apartment blocks, the Meskhetians lived in single-family homes in easily identifiable areas.

Envy was another factor: The hard-working Meskhetians were better-off than most Uzbeks. Many worked as traders or small businessmen, positions that brought them directly into conflict with the Uzbek mafia.

When gangs of Uzbek youths appeared in Kokand's Meskhetian neighborhood armed with metal bars and molotov cocktails, Vezirov and his neighbors took refuge in a nearby garage. Interior Ministry troops saved them from the crowd, but did nothing to protect their property. The mob looted the houses, carting away furniture, TV sets and videos, and then set the whole area on fire.

None of the ringleaders has been brought to trial and it seems unlikely that any will be. Their precise identity is shrouded in mystery. Some blame the local mafia, operating in conjunction with corrupt Communist Party officials. Others say the violence was inspired by nationalist organizations benefiting from President Mikhail Gorbachev's policy of glasnost, or openness.

Whatever the reason for the disturbances, the result is clear. The pogroms served as a warning to Russians, Ukrainians and Jews that they could be next in line if the situation deteriorates.

"The Meskhetian Turks have practically all left. The Jews are going to Israel. The Germans are going to Germany. The Tatars are going to the Crimea. That leaves us Russians. We would like to go back to Russia, but fear that we won't get a very good reception. Things are worse there than they are here," said Boris Khatuntsev, a Russian journalist who has lived in Fergana for 24 years.

For millions of Russians who emigrated to Central Asia in the '50s and '60s, the region was a kind of Soviet sunbelt, a land of opportunity and promise. Even today, living standards for Europeans are appreciably higher out here than in Russia. Food is plentiful and relatively cheap. The sun shines most of the year, in contrast to the dreary six-month-long winters back home.

There is a wistfulness to conversations with Russians here: If only everything could go back to being the way it was. "It used to be that the top man was a Russian and his deputy an Uzbek," said a Russian official recently passed over for promotion. "Now the top man is an Uzbek and his deputy a Russian, with the Russian doing most of the work. In a few years' time, you'll see: Both men will be Uzbeks."

Now home to about 6 million people, the Fergana valley is one of the most densely populated regions of the Soviet Union. The pressure on land is so intense that an argument over irrigation rights or the ownership of a field can lead to dozens of deaths. Last summer's clashes in Osh began with an argument over a few acres of land between rival Uzbek and Kirghiz communities.

In an attempt to ease tensions, the Uzbekistan government recently announced that every married couple has the right to a private plot of about half an acre. But it is practically impossible to carry out the decree without disbanding state and collective farms, which Communist authorities are loath to do.

"There's not enough land for everybody," complained Abdullah Otabayev, a 63-year-old collective farmer from Kuvasai, the small town south of Fergana where last year's disturbances began. "And even if the government gives us the plots to which we are entitled, we will still need building materials."

Otabayev has 12 children, a medium-sized family by Uzbek standards. So far, he has managed to provide his two oldest sons with plots of land and houses of their own. When his five daughters marry, they will move out. For the time being, however, they are all living in the same mud-brick, four-room house -- along with his five younger sons, their wives and their children.

The collective farms of the Fergana valley have become prime recruiting grounds for rioters. According to the deputy head of the local KGB security police, Safar Kazakov, about 25,000 people participated in the anti-Meskhetian pogroms. Most were rural youths, poorly educated and underemployed, who were ready to listen to the tales of alleged Meskhetian atrocities spread by provocateurs.

The ethnic tensions in the Fergana valley have been compounded by the Kremlin's longstanding policy of divide and rule. Until 1924, the entire area was part of a single Central Asian state known as Turkestan. Stalin divided the valley among three newly created republics -- Uzbekistan, Kirghizia and Tajikistan -- to forestall any united opposition to Moscow.

"What we are seeing now is the direct result of Stalin's policies. He created a slow-fuse time bomb, creating many artificial nations out of what used to be essentially one people," said Abdusalom Ergashev, a leader of the Uzbek popular movement Birlik in Fergana.

Birlik supporters accuse the Kremlin of putting the Central Asian peoples at loggerheads with each other by emphasizing the linguistic and ethnic nuances among them. The result, they say, is that Uzbeks and Kirghiz have now become bitter enemies, even though they come from the same Turkic stock and have little difficulty understanding each other's language.

In the absence of hard statistics, there is a widely accepted measure of Soviet migration trends: shipping containers. Every day, some 200 containers packed with belongings leave Uzbekistan, heading northward across the desert to Russia. That works out to 73,000 families -- or about 200,000 people -- a year. In most regions of Central Asia, there is now reported to be a six-month wait to rent containers.

Not everyone, of course, is leaving. Out of Uzbekistan's 20 million population, at least 5 million are non-Uzbeks. Native Russian speakers are still a majority in Fergana, Tashkent and several other Central Asian cities. These people -- popularly known as "aliens" because they live outside their titular republics -- are the strongest source of potential opposition to the centrifugal forces now sundering the Soviet Union.

"It may sound crazy, but I don't want to leave. This is my home," said Sasha Feinberg, a Jewish screenwriter harassed by the KGB security police in the '70s because of his contacts with Westerners. "I see two possibilities that will allow us to stay here. Either there will be some kind of military coup. Or there will be a rapid transition to a market economy. Under a market, Uzbeks will not think of us so much as Jews or Russians, but as people who can provide them with useful services."

The exodus of Russian technicians and specialists has already created severe economic difficulties. Ambulance services are working at half-strength because of a shortage of doctors. Uzbekistan's largest electric power station, on the Syrdarya River, may have to cut back operations because there is no one left to service its giant turbines.

The "aliens" are far from a cohesive group. According to a recent opinion poll, one in three Russians living in Central Asia favors the region's secession from the rest of the Soviet Union.

The mixed feelings of many Russians about the loss of their internal "colonies" are a reminder of the unusual nature of the empire cobbled together by Stalin. According to Marxist textbooks, a metropolis is expected to exploit its colonies. In the Soviet Union, the imperial logic has been turned on its head.

"I visited my home region last year and I was appalled," said Khatuntsev, the Russian journalist. "The villages are deserted, the roads are terrible, there's nothing to buy in the shops. Life is better here. But at the same time, Russia is subsidizing all the other republics with cheap oil."

"Russians live worse than us," agreed Akhat Mansurov, an Uzbek doctor and deputy mayor of Fergana. "In leading the rest of the Soviet Union to the verge of destruction, they brought the same fate on themselves. Can you call such a people colonialists?"