Russian warplanes buzzed the Chechen capital and explosions were heard northwest of the city early Sunday after Russia's deadline for the rebellious republic to surrender expired.

Five hours after the midnight (2 p.m. MST) deadline, Grozny was calm, but residents sought safety in bomb shelters and cellars or waited at home for civil defense officials to sound the alarm of an impending attack.Volunteers patroled Grozny's streets as Chechen fighters moved military equipment from the city center to the outskirts in preparation for a Russian attack, the ITAR-Tass news agency said.

Defense Ministry officials in Moscow refused to comment on the flights over Grozny and offered no explanation of the explosions. The Interfax news agency said the flights lasted about three hours then resumed after a two-hour break.

The agency also reported a rocket attack on the village of Pervomaiskoye northeast of Grozny 20 minutes after the deadline passed. There were no immediate reports of casualties.

With Russian tanks and troops poised to enter Grozny, Chechen President Dzhokhar Dudayev on Saturday offered last-minute talks with Moscow to end the fighting.

But Russian officials said it was already too late and threatened a missile assault on Grozny unless Dudayev's forces surrendered their weapons by midnight.

After the deadline passed, Chechnya's vice president, Zelimkhan Yandarbiyev, went on television and urged his people "to be courageous and calm in the face of the coming aggression."

Russian soldiers seemed reluctant to fight, even if it meant disobeying direct orders.

"If we get the order to move forward, none of us will go - we all prepared our letters of resignation two days ago," said a senior lieutenant who identified himself only as Viktor.

He was part of an armored column that stopped about 30 miles west of Grozny, the Chechen capital. The column commander, Maj. Gen. Ivan Babichev, said his tanks won't advance even if ordered to do so.

"If we send tanks against civilians, it'll be just like the Soviet Union - what if they did the same to my mother in Belarus?" Viktor said, shuffling his feet in large felt boots.

In a telegram to Russian President Boris Yeltsin, Dudayev said he would agree to peace talks "without any preliminary conditions," the ITAR-Tass news agency reported.

Dudayev was responding to a message earlier in the day by Yeltsin, who met with his hawkish Security Council in Moscow.

As evening fell, sporadic shelling could be heard on the outskirts of Grozny.

Deputy Prime Minister Nikolai Yegorov said missiles would be fired at strategic targets if steps aren't taken to disarm "illegal armed groups" by midnight.

If Dudayev "does not come to his senses after the strike, the groups will be destroyed," he told the ITAR-Tass news agency.

Chechen spokesman Movladi Yudugov shrugged off the threat.

"When the bombing starts, we will first go to our shelters. When it is finished, the command will go out to our forces to defend the city against the Russian attack," he said.

But the threat was the most serious challenge yet by Moscow to Dud-a-yev's regime.

Chechnya, a mostly Muslim region of 1.2 million people in the Caucasus Mountains, declared independence in 1991. Russia sent troops last Sunday to try to restore Moscow's authority.

Already, there are unconfirmed reports that hundreds of civilians are dead in the Russian offensive, along with at least 15 - and perhaps as many as 70 - Russian soldiers. More than 8,000 civilians have fled the advancing Russian troops, the Interfax news agency reported.

Babichev's armored column has withdrawn about a half mile from where it was stopped last week by peaceful demonstrators near the village of Dovidenko.

According to soldiers at the head of the column, officers agreed unanimously to disobey orders to move on the Chechen capital.

"A mutiny? You could call it that," said a lieutenant colonel from the 19th Motorized Infantry Division with a shy smile. Like other soldiers in the division, he spoke on condition of anonymity.

Officers said Babichev had been recalled to regional military headquarters in Mozdok.

If Yeltsin orders an attack on Grozny, it remains unclear how many soldiers will obey.

Some Russian troops northwest of Grozny have shown a willingness to use force, shelling outlying villages on the outskirts of the city.

But morale in the poorly paid Russian armed forces is low, and Russian Defense Minister Pavel Grachev is unpopular.