Security Council Votes to Tighten Sanctions Against Serbs : Bosnia: Despite news of a cease-fire, U.N. acts after rebels shell civilians in Srebrenica. Russia and China abstain.

The U.N. Security Council, furious over the defiant Serbian aggression in the eastern Bosnian town of Srebrenica, brushed aside news of a new cease-fire agreement late Saturday night and clamped new and tighter sanctions on the former Yugoslav federation.

The 13-to-0 vote--with Russia and China abstaining--came at the end of a day when the Bosnian Serbs, ignoring warnings from the Security Council, unleashed a major artillery barrage on civilians cowering amid the ruins of Srebrenica and blocked U.N. peacekeepers from going to their rescue.

Later in the night, the military commanders of the Bosnian Serbs and the Bosnian Muslims, meeting in Sarajevo, signed a cease-fire that guaranteed safe evacuation of civilians from Srebrenica. But the news did not impress the Security Council, which has met nothing but defiance from the Serbs during this latest stage of the civil war in Bosnia-Herzegovina.

The sanctions were imposed under the theory that the rump Yugoslav federation--made up of Serbia and Montenegro--has the power to pressure the Bosnian Serbs into halting their aggression. The sanctions would freeze all Serbian assets abroad and impose a system of monitoring and confiscating all ships, planes, railroad cars and trucks that try to bring goods into and out of Serbia.

There had been a fear that Russia would veto the sanctions. The Orthodox Christian and Slavic Serbian people are regarded as traditional allies in Russia, and beleaguered Russian President Boris N. Yeltsin’s opponents have been accusing him of betraying Serbia.

But Russian Ambassador Yuli Vorontsov, after conferring with Moscow, said he would abstain rather than obstruct the work of the Security Council. However, he called adoption of the resolution “quite untimely” and warned that the haste might lead to “possible negative consequences.”

Russia had warned the Serbs on Saturday that if there was no breakthrough in peace talks, the Kremlin would not veto tougher U.N. sanctions.

Yeltsin’s personal envoy to the region, Deputy Foreign Minister Vitaly Churkin, has traveled several times to Belgrade to meet Serbian leaders to try to win their backing for a peace plan proposed by mediators Cyrus R. Vance of the United Nations and Lord Owen of the European Community. But Churkin indicated to the Itar-Tass news agency on Saturday that his efforts had been unsuccessful.

The sanctions will not go into effect until April 26, a day after the Russian referendum on the rule and economic policies of Yeltsin. Out of deference to Yeltsin’s domestic troubles, the Security Council had originally agreed to defer voting on the sanctions until after the referendum.

But the Serbian onslaught on Srebrenica while everyone waited for the Yeltsin referendum amounted to a brusque and contemptuous back of the hand to the Security Council. Prodded by the smaller members and by France, the Security Council finally decided the waiting only made it look ineffectual and foolish.

The Bosnian Serbs’ fierce storm of mortar and small-arms fire was aimed at Srebrenica’s center, where Muslim women, children and elderly are trapped by the Serbs’ yearlong siege, said an official at U.N. mission headquarters in Zagreb, Croatia. Sniper fire was reported from Serbian gunmen positioned only a few hundred yards from the town center.

One shell smashed into the post office building occupied by humanitarian relief workers and the handful of U.N. troops in Srebrenica, making clear that the Serbian gunners were deliberately targeting civilians, the official said.

Twelve people were confirmed dead from the attack, but the toll was expected to rise once the barrage subsided enough to allow collection and treatment of the victims, said U.N. mission spokeswoman Shannon Boyd.

A U.N. aid convoy that had sought to take in food and help evacuate the defeated community’s terrified population was turned back by the offensive.

In Washington, Clinton Administration national security officials met Saturday to discuss what one knowledgeable official called “a full range of options,” including military and diplomatic steps that the United States could take next in the crisis.

President Clinton came under new congressional pressure to take military action, as Senate Minority Leader Bob Dole (R-Kan.) urged Clinton to issue a “pull back or else” ultimatum to Serbia. If the Serbs do not withdraw their troops within 24 hours, Dole said they should face airstrikes by NATO warplanes.

Boyd said in Sarajevo that the two rival military commanders agreed on a halt to the fighting in Srebrenica. Gen. Ratko Mladic, commander of the Bosnian Serb forces, and Gen. Sefer Halilovic, Bosnian government commander, signed a cease-fire that was to take effect early today, she said. The cease-fire would coincide with the start of Orthodox Easter.

Srebrenica, which has come to symbolize Bosnia’s losing battle against Serbian nationalists bent on capturing most of the republic for a Greater Serbia, was designated a “safe area” by the Security Council late Friday in hopes of protecting the tens of thousands of refugees and residents until their evacuation can be organized.

The U.N. resolution demanded the withdrawal of Serbian forces encircling the town and that they allow an armored company of Canadian peacekeeping troops to deploy to monitor “the humanitarian situation in the safe area.”

An advance party of 45 Canadian troops set off for Srebrenica from the Bosnian government stronghold of Tuzla but was blocked at the first Serbian checkpoint, U.N. sources said.

U.N. Protection Force commander Gen. Lars-Eric Wahlgren met with Mladic and was given renewed assurances that the Bosnian Serb forces would comply with the Security Council orders.

But aid agency officials and some U.N. sources complain privately that Mladic’s word has repeatedly been shown to have no relation to the actions of those under him.

“This is the second time in a week that the force commander has sat down with Ratko Mladic and listened to his words of reason while his guys were at the same time firing on civilians in Srebrenica,” said one angry U.N. official.

The Office of the U.N. High Commissioner for Refugees sent nine trucks carrying food and medicine bound for Srebrenica and had intended to evacuate some of the sick and wounded to Tuzla, about 45 miles to the northwest, spokeswoman Lyndall Sachs told reporters in Belgrade.

But the convoy was halted by rock-throwing Serbs as soon as it crossed into rebel territory on the Bosnian side of the Drina River, a U.N. source said. One truck driver had to be hospitalized.

Elsewhere in ravaged Bosnia, extremist Croatian forces took advantage of the West’s focus on Srebrenica to wage their own nationalist power struggle. U.N. reports told of rocket and grenade attacks in Vitez, Jablanica, Busovaca and other towns where the once-allied communities are mixed.

Meisler reported from the United Nations and Williams reported from Split, Croatia. Staff writer John-Thor Dahlburg of The Times’ Moscow bureau contributed to this report.