Russian troops launched a major ground offensive into the separatist southern region of Chechnya today with the apparent aim of creating a buffer zone to block infiltration of Chechen guerrillas into neighboring parts of Russia, according to Russian and Chechen officials.

It appeared to be Moscow's most powerful military operation against Chechen guerrilla forces since 1996, when the Chechens forced Russian troops to withdraw from the region in disorder and defeat after a brutal two-year conflict that left the rugged Caucasus territory virtually independent of Moscow.

Russian leaders threw a blanket of secrecy over the new offensive, but Prime Minister Vladimir Putin hinted strongly that it had begun, adding that Russian troops in fact had been fighting just inside the Chechen border for two weeks. "Military operations are already underway in Chechnya; Chechnya is Russian territory, and our troops can move anywhere," he declared.

The chairman of parliament's Defense Committee, Roman Popkovich, said that "certain essential villages are being taken; certain operational space is needed to rule out . . . counterattacks."

Putin suggested that the aim of the offensive is limited -- to establish a kind of Maginot Line inside Chechnya to prohibit the guerrillas from operating in adjoining Russian regions -- as they have in Dagestan since late August. "We need to answer a very important question: Where do we want to establish this safety zone?" he said. "Shall we do it on our territory? Will we wait for them to come again and capture our villages? . . . I don't think it expedient."

The idea of occupying a portion of Chechnya -- which lies about 1,000 miles south of Moscow -- suggests that Putin may have a long-term plan for resolving the lingering conflict with the Chechens. Indeed, some Russian observers speculate that the goal may be to reclaim and secure a defensible part of Chechnya and let the rest -- the remote mountainous area to the south -- go its own way.

An analysis of the operation by the Interfax news agency indicated that Russian forces intend to hold a line at Chechnya's Terek River, keeping the guerrillas at bay in the southern highlands -- an area that became a guerrilla stronghold during the 1994-96 war. "There is a plan for [driving the] militants into the mountains and localizing them there," said Popkovich, the legislator.

Taking control of all of Chechnya, which the Russians tried in the earlier conflict, seems not to be under consideration. "It would entail numerous casualties," the Interfax report observed. Rather, it said, Russia will "determine its own state border with Chechnya" then expel the region from the Russian federation.

Mairbek Vachagaev, the chief Chechen representative in Moscow, said Russian troops had penetrated 12 miles into Chechnya from positions along the northern border -- an area of flat terrain suited for tank formations and large-scale maneuver. Russian news reports said the troops had advanced six miles into Chechnya, then withdrew to a defensive line three miles farther back.

Vachagaev warned that a Russian occupation of any portion of Chechnya is a formula for perpetual warfare. "We are people who fight for each square meter of our land," he said. "The Russians seem yet not to understand who they are dealing with."

In any event, the new ground assault is sure to provoke trepidation among Russian citizens, who were horrified and astonished by the ineptness of their military force during the previous war, as ill-trained, ill-equipped recruits were thrown into battle and thousands were killed or wounded. The Russians bombed and shelled Chechen cities, towns and villages in an effort to crush the separatist guerrillas, but killed tens of thousands of civilians instead.

Public opinion polls have shown support for concentrated Russian airstrikes on Chechen factories, bridges, oil depots and frontier towns that began last week, but it remains uncertain if that support will extend to a land war.

The eight-day-old air campaign was initiated to punish Chechnya for the recent guerrilla raids into the neighboring Russian region of Dagestan, where they had vowed to set up an Islamic republic, and for a series of devastating bomb attacks on apartment buildings in Moscow and two other Russian cities that left 300 people dead. The Kremlin has insisted the bombings were sponsored by the guerrillas, but both they and the Chechen government deny any role in the attacks.

Chechen officials say that dozens of residential areas have been hit by Russian bombs and that women and children are among hundreds of casualties. At the same time, at least 80,000 Chechen civilians have fled their homes for the neighboring Russian region of Ingushetia, where officials say they have few resources to care for them.

"The Russians are trying to make civilian life impossible," Vachagaev said. During an interview in his office, he displayed a letter to Putin from Chechen President Aslan Maskhadov in which Maskhadov complained that airstrikes on a refinery in Grozny, the Chechen capital, had filled the air with toxic debris. He asked that the Russians halt the attacks and help clean up the bomb sites. The letter was returned unanswered, Vachagaev said.

Chechen guerrilla commander Shamil Basayev -- who outmaneuvered the Russians time and again during the earlier war -- led last month's incursion into Dagestan, but he and much of his force ultimately retreated across the border under a Russian airborne and artillery bombardment. Putin has said that the Russian assault will end only when Chechnya renounces terrorist attacks and surrenders Basayev along with other accused "terrorists."

In Washington, State Department spokesman James P. Rubin said: "We're obviously concerned. . . . The current situation is heading in a negative direction that threatens the stability of the entire region. Taking action against terrorists is legitimate, but it can't be done in an indiscriminate way." Rubin said that the Clinton administration had expressed its concern to the Russian government.

Italy, France and Germany called for a "political solution" to the conflict, also citing concerns about regional stability. But Washington and its allies are hamstrung by deference to pro forma Russian sovereignty over Chechnya and by NATO's own actions during the Kosovo war. NATO airstrikes on Yugoslavia unintentionally killed civilians, making criticism of civilian suffering caused by Russian attacks difficult to sustain, especially when Russia insists it is protecting itself against terrorism.