LONDON (AP) _ Backed by a stiff NATO warning of possible military action, the Clinton administration and its allies today called for a negotiated settlement by mid-February to end the violence in Kosovo.

The six-Western powers of the Contact Group declared in a statement the Serbian province must be granted ``substantial autonomy.''

In a stern message to Yugoslav President Slobodan Milosevic, the foreign ministers said there were only a ``limited number'' of points requiring discussion.

The talks between the Yugoslav government and representatives of ethnic Albanians from the province would begin Feb. 6 in Rambouillet, France, and end within seven days. Robin Cook, the British foreign secretary, and his French counterpart, Hubert Vedrine, were picked to lead the negotiations.

In the meantime, the statement adopted by the United States, Britain, France, Germany, Italy and Russia said the Serbs must stop ``all offensive actions/repression'' in Kosovo and promote the safe return of the thousands of civilians displaced from their homes as a result of the conflict.

Another demand leveled at Belgrade included a war crimes investigation of a reported massacre of 45 ethnic Albanian civilians two weeks ago in Racak, in southern Kosovo. The allies also want the suspension of Serb officers operating in the area at the time, until the results of the probe become available.

Further, they want Milosevic to reduce troops to the number he agreed upon last October in a ceasefire arranged by U.S. mediator Richard Holbrooke.

The ministers said the Kosovo Liberation Army shared responsibility with Yugoslavia's security forces for the escalation of violence in the province. They said both sides would be held ``accountable if they fail to take the opportunity now offered to them'' to end the conflict.

Cook said he would fly to Belgrade on Saturday and then go to Pristina to present the demands to Milosevic and the ethnic Albanians.

``We expect them to respond, and I will make it plain that this is a summons to negotiations. And we expect them to turn up in good faith with the objective of reaching an agreement on the detailed work we have done,'' Cook said.

Meantime, in Yugoslavia today, police clashed with ethnic Albanian rebels in a village near the Albanian border, killing 20 guerrillas, Serb sources said. One policeman was also reported killed in the village of Rogovo.

The allies are hoping to use the threat of military action to help end the crisis.

``NATO stands ready to act and rules out no option,'' Secretary General Javier Solana said Thursday in Brussels, Belgium. ``We are ready to act if necessary.

To add weight to the drive for international peace talks, France and Britain said in a joint statement Thursday they would commit ground troops to Kosovo as reinforcement for a political solution.

The U.S. plan being presented to the Contact Group on the former Yugoslavia would require Milosevic to negotiate terms of self-rule with ethnic Albanian leaders, withdraw troops and special police units from Kosovo, and permit the war crimes investigation.

The American formula provides for the two sides to set aside the independence issue for three years. The parties then could resume discussions on the province's long-term future.

In Washington, White House press secretary Joe Lockhart said Thursday the United States would continue to pressure Milosevic and the ethnic Albanian Kosovars to reach an agreement.

Cruising in the Adriatic Sea and standing armed and ready at allied airfields in Italy are dozens of ships and fighter planes primed to strike at Serb targets.

About 2,000 people died and nearly 300,000 were driven from their homes in seven months of fighting in Kosovo last year between the Kosovo Liberation Army and Serb forces. The conflict was halted only by the threat of NATO airstrikes last fall.

U.N. Secretary-General Kofi Annan has said a threat of force was essential to bring about a negotiated settlement.