Allies to Bolster Bosnia U.N. Units : Balkans: Major powers seek to prevent further humiliation at hands of rebel Serbs. U.S. official says use of Americans to help free hostages has not been ruled out.

Five of the world’s most powerful countries agreed early today to strengthen U.N. military forces in Bosnia-Herzegovina to give them the muscle to prevent further humiliation at the hands of rebel Serbs.

With U.S. Marines and their French and British counterparts heading for the Adriatic Sea and more than 300 peacekeepers held hostage in Bosnia, the foreign ministers from the Contact Group--the United States, Russia, France, Britain and Germany--said after a marathon five-hour meeting that the U.N. force must reorganize itself to eliminate the sort of isolated detachments that were easy prey for Serbian hostage-takers.

The ministers also said the U.N. force needs more troops and heavier weapons.

Britain has already alerted 6,000 troops, backed up by artillery and tanks, for deployment to the Balkans.

And a U.S. official said the possibility of using U.S. troops as part of a commando action to free the U.N. troops held as hostages by the Serbs has not been ruled out.

“Nothing is excluded,” he said. “Obviously, when you’re dealing with several hundred hostages in different locations, there’s no simple solution even with the best of commando plans that you might have. But nothing is excluded.”

At the same time, the five nations agreed to resume talks with Serbian President Slobodan Milosevic, offering to suspend--but not repeal--economic sanctions if Serbia recognizes the independence of Bosnia and other republics carved out of the collapsed Yugoslav federation.

U.S. envoy Robert Frasure will go to Belgrade later this week to restart the negotiations, which broke down last week over Milosevic’s demand that the sanctions be ended irrevocably.

Milosevic wanted the sanctions to be removed by the U.N. Security Council, which would have allowed Serbia’s ally, Russia, to veto any measure to reimpose the sanctions.

In the official communique, the Contact Group papered over the dispute by saying that “sanctions suspension should be finalized in the Security Council.” However, U.S. officials said the use of the term “suspension” preserves the U.S. demand to make sure Milosevic keeps any agreement that he makes.

In Brussels, French Foreign Minister Herve de Charette and British Foreign Secretary Douglas Hurd both indicated that the major powers were close to an agreement with Milosevic.

“We are quite close to an agreement between the Contact Group and Mr. Milosevic,” Hurd told reporters after a meeting of European Union foreign ministers in Brussels on Monday.

All five Contact Group ministers stressed that the U.N. force should remain in Bosnia. France, Britain and other countries contributing troops have suggested that they might withdraw their soldiers unless steps are taken to protect them. The ministers said the recommended steps should ensure the security of the force.

Although U.S. officials said that the North Atlantic Treaty Organization probably will hold off on additional air strikes until the effectiveness of the planned reinforcement of the U.N. force can be tested, Secretary of State Warren Christopher told a joint news conference: “The use of air power must remain an option.”

None of the ministers disagreed publicly with Christopher, although Russia has consistently opposed bombing of Bosnian Serb targets. Russian Foreign Minister Andrei V. Kozyrev told the news conference that the Contact Group put its priority on “political action and not military solutions.”

Before the meeting began Monday night, the United States, Britain and France were moving military units into the area, ready to give the beleaguered 22,000-member U.N. force there the muscle needed to take the offensive.

About 2,000 U.S. Marines were pulled off exercises around the island of Sardinia and sent to the Adriatic. The U.S. aircraft carrier Theodore Roosevelt, accompanied by the cruiser Hue City, was on its way to the Adriatic, as was the French aircraft carrier Foch.

British Defense Secretary Malcolm Rifkind said the decision to triple Britain’s presence was intended as a “clear and unmistakable message” to the Bosnian Serbs who are holding 33 British peacekeepers hostage along with more than 300 other U.N personnel.

In their stronghold of Pale, near the Bosnian capital of Sarajevo, the Bosnian Serbs showed no signs of backing down. Leader Radovan Karadzic and his army’s supreme command voted Monday to cancel all U.N. resolutions to which they had been a party because the United Nations “interfered in the war and allied with our enemies.”

The Serbian leadership also prohibited the United Nations from changing its mandate without Serbian approval, banned unauthorized flights over Serbian airspace and vowed to regain full sovereignty over all its territory.

The Serbs’ actions had already effectively ignored U.N. resolutions, which included the banning of heavy weapons around U.N. “safe areas” in Bosnia, but the announcement Monday showed that the Serbian leadership does not plan to negotiate.

There were no reports Monday of additional peacekeepers falling under Serbian control. The total number of hostages stood at around 370, and Bosnian Serb television from Pale took pains Monday night to broadcast pictures of the peacekeepers seated at tables eating, like a scene from any mess hall.

Also, Bosnian Serb army commander Gen. Ratko Mladic said that the men would no longer be chained but will remain in the areas of potential NATO targets until the alliance promises not to launch additional bombing raids.

There were other ominous signs of Serbian war preparations. Bosnian Serb soldiers continued to loot U.N. equipment, U.N. officials said. In addition to 200 heavy weapons seized during the weekend, they have stolen a total of 36 armored vehicles, including six light tanks, all of which bear U.N. insignia.

Also Monday, hundreds of grieving people gathered at a pre-dawn funeral for the mostly teen-age and twenty-something victims of last week’s Serbian shelling attack on the U.N. “safe area” of Tuzla.

The shelling Thursday of a sidewalk crowded with cafes claimed 71 lives and came in retaliation for NATO air strikes earlier that day.

Muslims and Catholics bearing candles joined in a cemetery to bury 48 of the dead in a funeral held in darkness to avoid becoming a target for another Serbian rocket attack.

“Our message to the world is no one should ever have to bury one’s dead at the crack of dawn,” a bitter Mayor Selim Beslagic said.

Kempster reported from The Hague and Wilkinson from Belgrade. Times staff writer Tyler Marshall in Brussels contributed to this story.