UNDER SIEGE.

IN 1996, REBELS IN CHECHNYA BEAT THE RUSSIAN ARMY. BUT NOW RUSSIA IS DETERMINED TO WIN.

In the Russian town of Mozdok, residents do not have to look out their windows to know when the skies are clear. They can tell from the roar of Russian warplanes taking off to bomb the neighboring province of Chechnya.

For the second time in five years, Russian troops are hammering Chechnya, trying to prevent the province from becoming an independent Islamic state. The war pits the massive Russian army against a small band of rebels. But the outcome of the battle is far from certain. Hanging in the balance may be the fates of Russia's new president, its fragile democracy, and its relations with the United States and Europe.

Chechnya has a long history of bloody battles with Russia. Located on the north slope of the Caucasus mountains between the Black and Caspian seas, it has rich oil reserves and is strategically vital for its access to the two seas. Unlike the Slavic, Christian Russians, the Chechens trace their roots to the ancient people of the Caucasus. They are darker-skinned, and overwhelmingly Muslim.

ROOTS OF THE CONFLICT

Russia first invaded the region in the early 18th century, and forcibly annexed it in the 1870s. When Chechen separatists rebelled during World War II, Soviet leader Joseph Stalin deported more than a million people from the region to Siberia and Central Asia, on the pretext that they had collaborated with Nazi Germany.

Rebellion flared again when the Soviet Union collapsed in 1991. As various republics of the former Communist state declared themselves independent, so did Chechnya, part of the Russian republic. But Russia refused to recognize Chechen independence, asserting its authority over the region.

In 1994, Russian troops invaded Chechnya, seeking to smash the independence movement and establish a pro-Russian government. Expecting a quick, easy victory, the military was instead met with surprisingly feisty resistance. After two years of heavier and heavier casualties, the Russian army made a humiliating retreat.

Three months ago, the Russian military launched a new campaign, after Moscow suffered a string of terrorist bombings believed to have been the work of Chechen militants. Amassing 100,000 troops to fight an estimated 12,000 rebels, the military has waged a scorched-earth battle in Chechnya, smashing civilian targets and rebel strongholds alike. More than 200,000 Chechens have fled their homes, and Chechen officials say more than 4,000 civilians have been killed.

U.S. CONDEMNS ACTIONS

The brutality has led to an international outcry over human rights abuses. U.S. and European leaders have condemned the war, calling for an immediate cease-fire. But Russian leaders say their military campaign against Chechnya is more justified than last year's bombings by Western nations in Kosovo. Says a U.S. official: "The Russians say, `When you hurt civilians in Kosovo, it was called collateral damage, and when we do that, you call it a violation of human rights.'"

If Russia were to lose the Chechen province with all its oil riches, Russia's battered economy would suffer a serious blow, experts say. And a Chechen victory could encourage other ethnically distinct provinces to seek independence as well.

The early success of Russia's campaign has bolstered the political fortunes of its new president, Vladimir Putin, who initiated the new military effort. But lately the campaign has begun to bog down, as the rebels have shifted their base into the rugged, mountainous south and the streets of Grozny, the capital. If the fighting drags on and Russia begins to suffer more casualties, the war could become unpopular, turning the public against Putin. Or it could lead Putin to assume more control, threatening Russia's fledgling democracy.

Chechen President Aslan Maskhadov warns that Moscow will end up in a quagmire, as the U.S. did in Vietnam. "Even if the war goes on for 10 years," he says, "Russia will not be able to conquer Chechnya and its people. Its action will lead it nowhere."

RUSSIA'S JOURNEY

1945-1989: The Cold War pits the Communist Soviet Union against the capitalist West. Tense showdowns occur in Berlin and Cuba. Soviet allies fight the U.S. in Korea and Vietnam.

1985: Soviet leader Mikhail Gorbachev comes to power and initiates reforms known as perestroika, but the arms race with the U.S. is bankrupting the country.

1989: The Berlin Wall, which for 28 years divided Soviet-controlled Fast Berlin from capitalist West Berlin, comes down, marking the Cold War's end.

1990: Capitalism arrives: The first McDonald's opens in Moscow.

1991: As Soviet republics revolt, discontented voters choose reformer Boris Yeltsin in Russia's first presidential election. Gorbachev resigns, and the Soviet Union is dissolved.

1999: Yeltsin resigns on December 31.

With reporting by MICHAEL R. GORDON in Chechnya.