Clinton Warns Serbs Against New Offensive in Bosnia : Muslims: NATO air strikes remain a live option, the President says. Christopher urges that the Muslims’ territorial demand be met.

President Clinton, clearly trying to head off a renewed offensive against the embattled Muslims of Bosnia-Herzegovina, warned the Serbs on Thursday that “the NATO military option is very much alive.”

The warning of possible air attacks against Serbian positions by North Atlantic Treaty Organization forces came as Secretary of State Warren Christopher chastised both the Serbs and Croats for the collapse of the peace talks in Geneva on Wednesday. He urged the Serbs and Croats to accept the Muslim demand for more land in a proposed Bosnian confederation of three ethnic states.

Both the President and Christopher called on all sides to return to negotiations to work out a treaty. But a U.N. official said that former Norwegian Foreign Minister Thorvald Stoltenberg, one of the mediators, believes there is no chance for quick resumption of talks.

Stoltenberg has reported that he now expects the war to intensify, with thousands more dying, the official said. “I am surprised that the secretary of state has blamed the Serbs and Croats,” said the official, who closely follows U.N. peacekeeping activities in the Balkans. “The Muslims should have accepted the deal.”

Under the proposed treaty, mediated by Stoltenberg and Lord Owen, a former British foreign secretary, Bosnia would be divided into three confederated states with Serbs controlling 52%, Muslims 31% and Croats 17%. This would give the Serbs much but not all of the land that they have conquered and “cleansed” of Muslims in the war that has raged for 17 months.

Speaking with reporters before conferring with Russian Prime Minister Viktor S. Chernomyrdin, Clinton described the Geneva negotiations as stalled, not collapsed. “The United States will do everything we can in the next few days to get the parties to resume the talks in good faith,” Clinton said.

The President then warned: “If, while the talks are in abeyance, there is abuse by those who would seek to interfere with the humanitarian aid, attack the protected areas and resume the sustained shelling of Sarajevo, for example, then I would remind you that the NATO military option is very much alive.”

Under plans drawn up by NATO, aircraft of the alliance could bomb Serbian positions to protect U.N. stations and relief convoys, subject to U.N. approval.

The U.N. official said that Gen. Jean Cot, the French officer in charge of U.N. forces in the former Yugoslav republics, and Adm. Jeremy Michael Boorda, American commander of NATO forces in Southern Europe, have worked out a system of instantaneous consultation whenever bombing is contemplated. The United Nations fears that bombing could expose its peacekeepers to accidental attacks by misfiring planes and to retaliation from angry Serbian troops.

If the United States decides to propose bombing of Serbian headquarters and depots as a means of breaking the siege of Sarajevo, it must get new authorization from the United Nations to do so.

Christopher told reporters he had “instructed that messages be sent to the Serbs and the Croatians indicating . . . that they should work toward greater flexibility in considering the adjustments asked for by the Bosnian government.”

He said that with agreement apparently close, it would be tragic for the parties to give up on negotiations with winter not far away. “If the settlement breaks down because of the stubbornness or the intransigence of the Serbs or the Croats,” he said, “the world community will certainly hold them responsible.”