Bosnian Serb’s Departure Slows Talks : Diplomacy: But Radovan Karadzic reportedly agrees to return if needed. New offensive launched in Sarajevo.

The wearisome difficulties of negotiating a peace settlement intensified Thursday as the Bosnian Muslims launched an offensive in Sarajevo and Bosnian Serb leader Radovan Karadzic abruptly decided to leave New York.

Reports of the offensive, coming only one day after the Clinton Administration announced its peace plan, prompted U.N. Secretary General Boutros Boutros-Ghali to scold the Muslim-dominated Bosnian government and to urge all sides in the murderous civil war “to pursue their objectives in the framework of the negotiating process rather than on the battlefield.”

After canceling a news conference for the second time in two days, Karadzic informed Cyrus R. Vance, a former secretary of state, U.N. special envoy and co-chairman of the peace talks, of his plans to leave immediately. The Serbian leader, according to Fred Eckhard, Vance’s spokesman, said he had “urgent business back home.”

Vance, while noting that Karadzic would probably not be needed in New York until the middle of next week, asked for and received a commitment from the Serbian leader to come back whenever needed, the spokesman said.

Another factor could have persuaded Karadzic to take a respite from New York: Demonstrators have gathered around his hotel in Manhattan denouncing him as a war criminal. The Reuters news agency quoted his wife as saying that the hotel manager asked them to leave because the demonstrations were disturbing other guests.

This raised a delicate issue in the negotiations. Lord Owen, a former British foreign minister, a European Community envoy and co-chairman of the Bosnian peace talks, reportedly told European ambassadors earlier in the day that the anti-Serb rhetoric of Washington politicians, the American media and New York street demonstrators had hardened the Bosnian Serbs’ position. He said it made it more difficult for negotiators to deal with them.

According to reports reaching U.N. headquarters from the peacekeeping forces in Sarajevo, the Bosnian government launched its long-planned offensive with heavy artillery against the Sarajevo suburb of Ilidza near the U.N.-controlled airport. Bosnian Serbs were rushing tanks into the area to counter the offensive.

U.N. spokesman Joe Sills said four French soldiers had been wounded in the cross-fire, two seriously, and that the airport, the vital terminal for relief supplies to Sarajevo, had been closed.

A participant in a closed-door meeting among ambassadors from the European Economic Community reported that Lord Owen said, “If I were a Bosnian Muslim, I, too, would not be satisfied with the proposed peace settlement.” But, he said, the peace plan reflected the reality of the situation in Bosnia.

Muslims have complained that the proposed Vance-Owen division of Bosnia into 10 provinces along ethnic lines would reward Serbs for their aggression and accept their “ethnic cleansing” of former Muslim areas--the infamous practice by Serbs of ejecting non-Serbs from Serb-controlled areas.

Owen also reportedly told the ambassadors that both he and Vance still did not know the exact role of Ambassador Reginald Bartholomew, the onetime undersecretary of state and U.S. envoy to the North Atlantic Treaty Organization who was appointed by the Clinton Administration to represent the United States in the Bosnian negotiations.

In Brussels, Bartholomew said he would fly to Moscow on Friday to seek Russia’s help in working out a peace settlement. Vance and Owen are hoping that the Russian government will be persuaded to pressure the Bosnian Serbs into accepting the peace settlement.