Defense Minister Igor Sergeyev declared today that the Russian military will occupy Chechnya "for a long time and seriously" as the army launched a second phase of its month-long offensive aimed at driving separatist Chechen guerrillas out of populated areas and into the rebellious region's rugged southern mountains.

In the most direct remarks so far about Moscow's intentions in Chechnya, Sergeyev indicated that Russian troops are digging in and essentially would become an occupation force in the breakaway region--which lies in the northern Caucasus area, about 1,000 miles south of Moscow. Russian forces "have come to never leave," he said.

When it launched the offensive a month ago, the military said its objective was to close off Chechnya's borders to halt incursions by Chechen-based Islamic militants into the neighboring Russian region of Dagestan. Russian officials also blamed Chechen radicals for four recent apartment house bombings in Moscow and other cities that took nearly 300 lives.

Since then, however, Russian forces have moved far beyond that limited goal; they have seized the northern third of Chechnya and are now pressuring its two major cities from three sides and bombarding them heavily.

Although the campaign against Chechen guerrilla forces has been popular with the Russian public, fresh doubts are being voiced about whether the military can sustain a long-term engagement in Chechnya, especially as winter sets in. Thus far, the advance has been far different from that of December 1994, when tens of thousands of tank-backed Russian troops poured into the region to try to put down a Chechen bid for independence.

Back then, ill-prepared Russian troops ran headlong into fierce resistance in Grozny, the Chechen capital, that soon led to vehement public opposition to the war. Slow-moving Russian ground forces proved vulnerable to hit-and-run guerrilla tactics and suffered heavy losses, particularly in mountain warfare. Moscow withdrew its forces in 1996, and Chechnya has since been virtually self-governing.

This time, however, Russian troops have met only sporadic opposition. Moreover, Russian commanders say they are deliberately avoiding frontal confrontations with Chechen defenders. Instead, they are using such standoff weapons as missiles and pilotless drone aircraft to carry the fight to the Chechens, as well as warplanes and long-range artillery. Still, some analysts say it is only a matter of time before the Chechens regroup and begin staging new guerrilla attacks on the Russian forces.

The full scope of the death and destruction in Chechnya is difficult to determine, as most journalists have not had access to the hardest-hit areas. Russian officials said this week that the Chechens have lost 3,000 men, while the army has put the number of its own dead at 190. The Chechens say they have lost 47 combatants and killed 1,600 Russian troops. There are similar discrepancies over the number of civilian deaths and the extent of damage.

More than 170,000 Chechen civilians have fled the Russian attacks in Chechnya, the majority of them to Ingushetia, a Russian region that borders Chechnya on the west.

Sergeyev, who visited Russian front-line troops today, said the military will try to win the hearts and minds of the Chechen population. "I think that in general, the main task at this breakthrough stage is to [gain] the confidence of the Chechen people by our attitude, help" and administration, he said.

Sergeyev, whose visit was covered by Russian television, underscored Moscow's intention to keep troops in Chechnya indefinitely by taking note of a military construction project there, but without explaining its purpose. "This is going to be our flagship construction site," he said. "The term is set and tasks defined. I think that by June or July 2000," this will be the regular base of a regiment, he said.

Meanwhile, advancing Russian troops appeared to be carrying out pincer movements on the flanks of Chechnya's two largest cities--Grozny, the capital, and Gudermes, about 40 miles to the east. Russian commanders said they were trying to encircle the cities and squeeze the Chechen defenders out and into the southern mountains. Russian and Chechen accounts suggested that the drives had reached the outskirts of both cities.

Russian aircraft have flown 100 sorties over Chechnya in the past 24 hours, officials said, the largest number in a single day since the offensive began. The intense bombing--combined with heavy artillery and rocket fire--was described as the beginning of phase two of the campaign; in the initial phase, Russian forces occupied the northern third of the region, north of the Terek River. Now they have moved beyond the river toward Grozny and central Chechnya.

Thus far, the army has indicated it will not launch a direct assault on Grozny, hoping to avert the kind of bloody toll it suffered five years ago in a frontal attack on the capital. But the military said that Grozny is 80 percent surrounded, with only the southern approaches open, while Russian troops were said to be within 500 yards of Gudermes.

Sergei Arutyunov, head of the Caucasus department at the Institute of Ethnology and Anthropology here, expressed concern in an interview today about the military's deepening involvement in Chechnya.

"Seeds of hatred are sown, and they will give shoots," he said. "The military will keep developing the offensive in Chechnya, more people will die. . . . What is going to be the final outcome? Grozny will again be razed to the ground. . . . Rebels will be driven into the mountains. They will go underground, into caves and conduct guerrilla warfare. [Russian troops] do not know how to fight in the mountains."

"We will have Ulster; we will have [Northern] Ireland or even worse," he said. "We will have Palestine, maybe worse. For many years to come, Russia will be exposed to terrorist acts; people will be dying. Thousands of Russian soldiers will die in the assault on Grozny. Partisan war will be on, eternally."

Russian officials have said they believe Chechen forces are being supplied by international terrorist groups, and they suggested that cutting off these resources will end the hostilities. Sergeyev, describing what he said was the "military aspect" of the conflict, told reporters today that "a guerrilla war can continue as long as there is a 'feeding' of this war. If the feeding is taken away, it stops."