President Clinton cut short a weekend of golf and relaxation last night, returning to Washington from Camp David as his aides grappled with the question of how to react to yet another abrupt turn of events in Yugoslavia -- one that appeared to threaten the military and diplomatic victory that had seemed within the president's grasp.

There was no sense of panic or despair in the White House at the news that talks between NATO and Yugoslav generals over an end to the war had collapsed, officials said last night. They noted that Clinton himself had predicted there might be bumps in the road to a Serb withdrawal from Kosovo.

Still, one official said, Clinton decided to return from Camp David last night -- instead of this morning as originally planned -- because "it's going to be a busy week." "Frankly, people would have been surprised if this had been smooth sailing," one official said.

At the Pentagon, spokesman Kenneth Bacon said Yugoslav officials had demanded a delay in the entry of Western peacekeeping forces that was unacceptable to NATO, which has said that its troops should be allowed to enter the province immediately and that all Yugoslav forces should be withdrawn. He declined to specify the length of the delay or to say whether it hinged on other conditions being met first.

Bacon said that NATO, which continued bombing in Kosovo over the weekend and destroyed up to three dozen military vehicles and pieces of equipment, today will be trying to find a way to step up the air war even further. "The talks are in suspension and the air campaign is not," Bacon said.

National Security Council spokesman David Leavy said last night that Clinton had placed phone calls during the day to three key NATO allies: British Prime Minister Tony Blair, Canadian Prime Minister Jean Chretien and Italian Prime Minister Massimo D'Alema.

Leavy declined to say whether the calls indicated a heightened concern about the talks in Kosovo. "It's important to touch base with a number of the leaders about what the strategy is," he said.

Secretary of State Madeleine K. Albright was on her way last night to a meeting in Germany with the foreign ministers of the so-called G-8 -- the United States, Russia, Britain, Canada, France, Germany, Italy and Japan. Those nations had set out the principles for a Kosovo settlement.

Albright's spokesman, James P. Rubin, told reporters on the plane to Germany that she "will continue to make diplomatic efforts with our G-8 colleagues toward a peaceful resolution of this conflict."

Gen. Henry H. Shelton, chairman of the Joint Chiefs of Staff, and Secretary of Defense William S. Cohen had said earlier yesterday that NATO's one-week deadline for withdrawal might be extended by a day or two, but they could not accept deliberate attempts at delay.

Shelton confirmed that while NATO officials are demanding that Yugoslav troops complete their pullout of Kosovo in a week, Belgrade's representatives want more time.

"We, in fact, want to make sure that the extra time is for good reason," Shelton said on ABC's "This Week." "Want to get the Kosovars back in as soon as we can."

Cohen said that in the last 24 hours Belgrade had brought a contingent of higher-ranking three-star generals to the talks in an effort to work out details of the withdrawal.

"There's no negotiation taking place," Cohen said. "It is making sure that everybody understands exactly what must be done, so there is no misunderstanding. We don't want to find ourselves in a situation where there is confusion where they go, how they go, how fast they go."

John Mintz contributed to this report.