Russian troops seized a key rebel stronghold today in their drive to capture Grozny, the captial of Chechnya. The Russian military showed no signs of easing the offensive, despite a blast of international criticism over its ultimatum that residents flee Grozny or face intensified bombardment.

Russian officials said their forces ousted separatist rebels from Urus-Martan, a center of Islamic militancy 12 miles southwest of Grozny. The town had been battered by heavy air and artillery bombardments for several weeks. Russian television broadcast pictures of Russian tanks moving through a city in flames. Houses were destroyed, markets smashed, and bodies littered courtyards. The streets were abandoned.

The conquest of Urus-Martan helps to solidify the military's armored ring around Grozny. Grozny is a prize that Russian troops evidently plan to claim sooner rather than later--perhaps before parliamentary elections on Dec. 19. Prime Minister Vladimir Putin has staked his political future on success in Chechnya, a region of southern Russia, and is backing a slate of candidates in the vote. In recent weeks, the Russian drive had stalled at two key towns that flank Grozny: Argun to the east, and Urus-Martan.

With today's apparent victory in Urus-Martan and last week's in Argun, Yegor Stroyev, speaker of Russia's upper house of parliament, predicted that the war in Chechnya will end soon. "It is now necessary to get down to peaceful construction," Stroyev said.

Russia sent its forces into Chechnya in late September following incursions by Islamic rebels into the neighboring region of Dagestan, and apartment building bombings in Russian cities including Moscow that the Kremlin blamed on Chechen militants. Chechnya has effectively been independent since 1996, when Russian forces withdrew after a two-year war.

The ultimatum to evacuate Grozny--contained in leaflets dropped over the devastated capital on Monday--has drawn intense criticism from the United States, Western Europe and Islamic countries, and Russian officials have since played down the warning. But the pace of war has remained as intense as any time in the 10-week-old ground offensive. Russian reports said jets and helicopters flew 150 sorties in the past 24 hours, hitting targets in Grozny, Urus-Martan and Shali, and along roads refugees use to escape combat and bombardment.

There was no clear indication that civilians were streaming from Grozny in response to the ultimatum. A safe passage for refugees will not open until Sunday, the Interfax news agency said. It will have a capacity of only 3,000 refuge-seekers a day, meaning it could take two weeks to empty the city, depending on the number of people trying to get out. Russian officials say up to 20,000 people still live in Grozny, while the Chechens put the number at 40,000.

The Russians say they are setting up refuges for civilians in 23 towns and villages under their control. But human rights observers say it is uncertain whether civilians, hunkered in basements and bunkers, actually saw the leaflets warning them to leave. They also say many stragglers are old or infirm, or women struggling with children.

The leaflets contained a stark warning to Grozny's inhabitants that they risked certain death unless they left the city by Saturday. But Russian officials insist the ultimatum was not tantamount to a threat. "The aim of this statement is to prevent casualties among peaceful civilians and reduce losses among federal troops as much as possible," Putin said.

Russian infantry have penetrated the suburbs of Grozny, Russian and Chechen reports said. Russian forces thrust into the extreme northwestern Nadterechnaya district and also command heights in the Zavodskoi district in the western outskirts where they have positioned artillery, a Chechen spokesman said.

In a detailed analysis by the Interfax news agency, Russian military officials explained the intense bombing as a tool to cut off rebel escape routes. There is no intention "to be soft on the gangs or their accomplices in Grozny," the officials said.

Unlike the first Chechen war, Russian infantry will not storm the capital, officials said, since Grozny is laden with land mines and incendiary booby traps. Rather, the aim is to beat the rebels out of Grozny "by bombs, shells and missiles," Interfax said.

In a departure, the assault on Urus-Martan included a contingent of pro-Russian Chechen troops who have gathered under the banner of Beslan Gantamirov, Russian reports said. Until a few weeks ago, Gantamirov, a former Grozny mayor, was serving time in a Russian prison for embezzlement. President Boris Yeltsin pardoned him, and quickly named him head of the loyalist contingent.

About 500 Chechen rebels had defended Urus-Martan. Before the war, the city had been a center of kidnapping gangs. Russian officials said more than 50 rebels were killed in the past three days of fighting; they gave no account of their own losses. "The fighters abandoned their positions when it became clear that it was practically impossible to hold them, what with air raids and artillery fire going on around the clock," a Chechen spokesman said.

A weary-looking Russian tank commander, Lt. Col. Yuri Budanov, said in a Russian television interview that resistance was light, except for "snipers and mortars, which were a nuisance."

Both Chechen and Russian officials say that the rebels are withdrawing to the mountainous south, an echo of their tactics of the 1994-96 war, when they withdrew from the region's towns and cities and then launched a successful counterattack.

CAPTION: Residents and refugees collect water brought by truck to Goragorsky, 35 miles northwest of Grozny, the Chechen capital, where Russian troops are headed.