Allies Debate Options for Bosnia Relief : Balkans: Promised truce in Sarajevo collapses. Bush confers with top aides, but no decisions emerge.

Western powers stepped up their deliberations Friday on Bosnia-Herzegovina after the collapse of the Serbian-promised cease-fire in Sarajevo, and indications grew that they may soon consider military force if the situation there does not improve.

In Washington, President Bush summoned his top national security advisers to talk about possible options for flying humanitarian aid into the embattled city, but officials said later that they apparently reached no firm decisions.

National Security Adviser Brent Scowcroft was quoted as telling reporters after the session that “nothing is imminent”--at least for the next few days.

U.N. Secretary General Boutros Boutros-Ghali, en route to a meeting in Senegal, issued a statement warning that if the Serbs do not end their bombardment of the Bosnia-Herzegovina capital in 48 hours, he would have to “reassess” whether to ask for Western military help.

In Lisbon, the foreign ministers of the 12 European Community nations, who are meeting with the 12 EC heads of government, approved a statement of support for humanitarian aid for Bosnia-Herzegovina under U.N. auspices.

The combination of developments appeared to mark a last-minute push by the West to jolt the Serbs into complying with U.N. demands for a cease-fire in the beleaguered Bosnian capital, which has been under siege for three months.

Serbian commanders apparently had ordered their troops to stop firing early Friday, but the cease-fire quickly broke apart as the city once again fell victim to sporadic artillery fire from Serbian positions in the hillsides overlooking the capital.

The resumption of the Serbian siege dampened hopes by some observers that the city’s airport might soon be reopened to accept relief supplies. About 300,000 Muslim and Croat residents have been trapped in the city, and supplies are very low.

U.N. peacekeepers have insisted that the artillery barrage be silenced for at least 48 hours before they will begin flying in aid packages, and the Serbs promised Wednesday that they would comply with the request.

But on Friday, Canadian Maj. Gen. Lewis MacKenzie, commander of the U.N. peacekeeping force, reported that the Serbian militia had resumed its firing and was refusing to relocate its artillery to the areas that the U.N. forces had designated.

The developments brought the Western powers ominously closer to a decision over whether to use military force to quell the fighting--a possibility that looks increasingly likely in order to rescue the city’s sick and starving residents.

Secretary of State James A. Baker III told reporters Friday that the latest U.N. resolution “does not authorize the use of force,” and State Department spokeswoman Margaret Tutwiler said Washington was not yet prepared to propose any changes.

But Boutros-Ghali and other U.N. officials indicated that the U.N. resolution could be changed, possibly as early as next week--and may well be if the current last-ditch diplomatic effort does not work.

Boutros-Ghali also said in his statement that the situation in Bosnia had “deteriorated considerably” Friday, with Sarajevo subjected to new attacks by tanks and infantry and heavy artillery. He vigorously condemned the Serbian militia assaults.

Meanwhile, Serbian President Slobodan Milosevic sought Friday to distance himself from the bloody fighting in Bosnia, telling an interviewer on CNN’s “International Hour” program that his forces “don’t have one single soldier on the soil of Bosnia and Herzegovina.”

“The international audience is showered by a lot of wrong information,” he said. “We . . . Serbians are victims of a media war which is very well organized and very well paid.”

Milosevic also told the Associated Press that Western powers should not intervene militarily to open the Sarajevo airport, and he invited international observers to his republic to confirm that his government is not helping Bosnian Serbs, as Western officials contend.

But the State Department’s Tutwiler said Friday that the United States sees “no indication that Serbian forces are willing to cease their attacks, remove their artillery or place it under U.N. observation, despite their (promise on) Wednesday.”

In Lisbon, the foreign ministers’ statement will be considered by the 12 EC leaders today in the final session of their two-day summit.

The statement called for the reopening of the Sarajevo airport to permit aid shipments and added that this should be accomplished “hopefully peacefully,” without spelling out the consequences if this is impossible. The statement called on the Western European Union, composed of nine EC members, to study military options.

Throughout the day, the foreign ministers floated a variety of possible approaches to the crisis in Bosnia.

Italian Foreign Minister Gianni de Michelis suggested that a European military force open the Sarajevo airport and secure a corridor into the city to guarantee the safe delivery of EC aid shipments.

Other nations, including Britain and France, questioned that strategy.

“Europe has neither the aim nor the means to be a policeman in Yugoslavia,” said a spokesman for French President Francois Mitterrand.

British Foreign Minister Douglas Hurd proposed ejecting Serbia from all international organizations--it has already been evicted from many--if Serbian troops are not withdrawn from Bosnia by July 3.

On more administrative matters, with almost no discussion, the EC leaders reappointed Jacques Delors to two more years as president of the Community’s policy-formulating commission.

Pine reported from Washington and Havemann from Lisbon. Times staff writer Douglas Jehl in Washington contributed to this article.