Russian armor and infantry broke into central districts of Grozny today, battling separatist guerrillas in a three-pronged advance on the bitterly contested regional capital, according to Russian and Chechen reports.

The Russians were trying to blast snipers and rebel antitank teams out of their positions, rather than relying solely on airstrikes and long-distance artillery to clear a path. Russian forces were advancing from the northwest, east and southeast with the immediate goals appearing to be Minutka Square, a major intersection in south-central Grozny, and a bridge over the Sunzha River, which bisects the city.

Russian officials have been predicting a "final assault" on Grozny for several days, to drive rebels from the city and claim the only major Chechen urban center still outside their control. Aided by clear weather, ground-attack jets and helicopters flew 150 combat missions over 24 hours, hitting both Grozny and mountain routes to the south.

The seizure of Grozny would come at an opportune time for the government of Acting President Vladimir Putin. A string of battlefield setbacks had begun to prompt criticism of him in Moscow and threatened to become a political issue before March 26 elections to choose the successor to Boris Yeltsin, who stepped down as president on Dec. 31. News commentators have begun to question official casualty counts, and military analysts have warned of a prolonged war of attrition.

Since their first probes of the capital in mid-December, the Russians had been stalled at the city's outskirts and had gained control of only one district, Staropromyslovsky in the northwest. Elsewhere, Russian tanks and artillery dueled inconclusively with rebel snipers and their mobile mortar batteries. The Russians, beset by fog and fear of casualties, were reluctant to penetrate the city's many warrens of tangled streets and mid-rise buildings, which can serve as settings for ambushes.

Russian forces also have placed new emphasis on securing areas outside Grozny in hopes of preempting hit-and-run guerrilla attacks on stationary positions. Refugees reaching Ingushetia, the region to the south, spoke of intensified security searches of basements, expulsions of women and children, and of Chechen men being rounded up in Grozny suburbs.

Taking Grozny involves long-term risks for Moscow. In the first Chechen war, from 1994 to 1996, the capture of the city began a long period of guerrilla harassment of Russian outposts throughout the capital. The Chechens also took hostages elsewhere in Russia and weakened Russian resolve to pursue the war. Eventually, a rebel counterattack drove the Russians from the capital, and the Chechens won de facto--albeit chaotic--independence.

Russian officials said that combat raged throughout Grozny today. "The decisive phase of the liberation of Grozny has started," said Konstantin Kukharenko, a Defense Ministry spokesman. Interior Minister Vladimir Rushaylo predicted the offensive will succeed "in the next few days."

Much will depend on the strength of rebel resistence, an issue on which officials of Chechen President Aslan Maskhadov's government have issued mixed signals. "The period of battles for strategic positions is coming to an end; from now on the tactic of a partisan war will mainly be used," Chechen Defense Minister Magomed Khambiyev said recently.

Aslambek Ismailov, a deputy rebel commander, said Russian forces made no progress today, although he described fierce combat at a Grozny cannery.

Russian television broadcast scenes from Grozny that looked like footage from World War II. Clouds of black smoke and dust rose high into the air as Russian tank and artillery shells crashed into crumpled buildings. As the long-range weapons poured fire into the city from heights to the north and the plains spreading out from the rest of the city, Russian snipers moved gingerly through twisted ruins, taking cover behind mounds of loose brick.

Over the past few days, Russian officials have issued official death counts of eight or nine soldiers daily, while estimating rebel fatalities at eight times that number.

Taking the capital, and a few mountain hamlets south of it would permit Putin's interim government to declare a key task accomplished--the freeing of most of Chechnya from rebel control. It would still leave another prime objective unfinished--the elimination of bands of rebels Moscow says pose a threat to Russia.

In a televised interview, Anatoly Kulikov, the Russian commander during the previous war in Chechnya, warned of prolonged anti-guerrilla combat. "I am afraid this conflict is our Ulster," he said, referring to Britain's decades-long battle in Northern Ireland. "It's for many years to come."

He suggested two remedies: Either pursue the rebels with rapid reaction forces or divide Chechnya in half, pacifying the northern flatlands and leaving the area south of the Sunzha mountain range to the separatists. As for Grozny itself, he prescribed its virtual destruction to end the threat of ambush.

Hints that Grozny will remain a derelict ruin have been floated or weeks. Moscow has sent its special envoy to Chechnya, Nikolai Koshman, to the city of Gudermes, Chechnya's second-largest, to set up a provisional capital, and on Sunday he declined to rule out the abandonment of Grozny as Chechnya's administrative center. "We have to free Grozny from the rebels and study the extent of damage first. After that, we will be able to talk about Chechnya's future capital," he said.