U.N. Chief Warns Serbs of Offensive : Bosnia: If peace talks fail, troops will be sent to force rebels out of Muslim and Croatian territory, Boutros-Ghali says. His remarks are a departure from U.S. position.

U.N. Secretary General Boutros Boutros-Ghali warned Sunday that if Serbian troops do not withdraw from Muslim and Croatian territory in Bosnia once diplomatic efforts have been exhausted, the United Nations will send troops to force the Serbs out.

“We have as an objective the withdrawal of the Serbs, and if they will not withdraw, then we’ll have to take the necessary measures,” Boutros-Ghali declared during an interview on ABC’s “This Week With David Brinkley.”

“I believe that if, after whatever ought to be done, we find that we are not able to obtain their (the Serbs’) withdrawal, then there is only one solution, which is enforcement,” he warned. He said U.N. members then “must be ready to send troops on the ground.”

Boutros-Ghali’s remarks--the first time he has suggested that the United Nations might launch offensive military action if the Serbs do not withdraw--were designed to intensify pressure on the Bosnian Serbs to sign a peace agreement with Croats and Muslims.

They also marked a significant departure from the position of the Clinton Administration, which believes that the United Nations should send troops only to help enforce whatever peace agreement ultimately is signed--not to drive back the Serbs.

It was not immediately clear how the United States ultimately might respond to Boutros-Ghali’s suggestion. The secretary general frequently has floated ideas that appear to exceed current thinking in the United Nations, partly as a way to press the major powers forward.

Defense Secretary Les Aspin, who appeared on the program a few minutes after Boutros-Ghali, reiterated that all that President Clinton has agreed to do is let the United States take part in a multinational peacekeeping expedition to help enforce a peace accord.

“Current policy is to use heavy diplomatic pressure . . . and we ought to give that a chance,” Aspin said. Asked about the possible use of force if the peace talks break down, he replied: “I don’t think we’re in a position to . . . talk about that at this point.”

Boutros-Ghali’s remarks followed reports that the United Nations is making plans to assemble a force of up to 50,000 heavily armed peacekeeping troops--to be coordinated by the North Atlantic Treaty Organization--to help enforce any peace agreement that may emerge from current negotiations.

The plan has been in the works for several weeks, but until now officials had not disclosed specific estimates of the probable size of the peacekeeping element. The U.S. role in such a force still is uncertain. Clinton has pledged to support that kind of operation but has not spelled out precisely to what extent.

Peace talks have been under way at U.N. headquarters all this past week, but so far agreement has been elusive. Bosnian Muslims and Serbs have both rejected a proposal by international mediators to split the country into 10 semiautonomous provinces.

Alija Izetbegovic, Bosnia’s Muslim president, was back in Sarajevo on Sunday to confer with other Bosnian leaders. On Saturday, Mate Boban, leader of the Croatian faction, said he was “positive” that Izetbegovic would sign the peace proposal when he returned.

Meanwhile, U.S. officials say that Serbian forces are continuing their drive to capture more Muslim-held territory in Bosnia before the peace negotiations approach a climax, tightening their grip on the Muslim enclave of Tuzla and raising new fears of a mass exodus of Muslim refugees.

Sandy Berger, President Clinton’s deputy national security adviser, told CNN’s “Newsmaker Sunday” that the Serbs are “trying to alter the situation on the ground to the extent they can in a particularly brutal and vicious way.”

Nevertheless, Berger declined to endorse suggestions that the West abandon the talks and mount an offensive to drive back the Serbs. He said that, instead, the allies will continue to tighten economic sanctions against Serbia and back the peace negotiations.

Aspin and Boutros-Ghali appeared to disagree Sunday on what role U.S. forces would play in Somalia once the peacekeeping effort there is placed under U.N. command sometime in late May or early June.

The secretary general spoke about American troops being involved in efforts to build a viable government in Somalia but Aspin, asked about that later, said it was “a little unclear” to him what Boutros-Ghali was talking about.

He said that U.S. forces have been in the country “to just start the flow of (food and medical) supplies.”