Even if President Slobodan Milosevic has genuinely accepted NATO terms for ending the war in Yugoslavia, the agreement reached yesterday marked the beginning of a peace process, not the end.

The key to ending the conflict lies in carrying out the agreement, U.S. officials stressed. "We're going to be looking for implementation, implementation and implementation, because it is only implementation of NATO's conditions that will lead to a peaceful resolution of this crisis," said the State Department spokesman, James P. Rubin.

First and foremost, Yugoslav troops must withdraw from Kosovo to convince NATO that Milosevic is serious about honoring the agreement. Under terms delivered by the Russian peace envoy, former prime minister Viktor Chernomyrdin, and Finnish President Martti Ahtisaari, his European Union counterpart, Yugoslavia must accept a timetable providing for removal of its air defenses from the battered Serbian province within 48 hours. Within the following seven days, all Yugoslav forces must pull out.

NATO officials said alliance military strategists have already marked out routes for the Yugoslav troops and Serbian police to pull out of Kosovo and are prepared to assure the Serb forces that they would not be bombed while they retreat. Kosovo is the southernmost province of Serbia, the dominant republic in the Serb-led Yugoslav federation.

Yugoslav military leaders are to meet NATO officers "within the next day or two" to discuss the departure, Defense Secretary William S. Cohen said on "PBS/The News Hour" last night. Officials said the military-to-military negotiations will bypass Milosevic, who has been indicted for crimes against humanity by the International Criminal Tribunal for the former Yugoslavia in The Hague.

"This military technical agreement has to be agreed during the time of withdrawal," said Ahtisaari. "We are talking about days, rather than weeks."

Only after substantial numbers of Serb troops leave would there be a pause in the bombing campaign, NATO leaders said.

"NATO intends to continue the airstrikes until Milosevic and the government of Yugoslavia convincingly demonstrate that the fighting is over, that Serb forces are withdrawing . . . At this point, not a single Serb solder has withdrawn from Kosovo," said Cohen.

But Chernomyrdin, who has pressed all along for an immediate bombing moratorium, insisted the airstrikes should stop as soon as NATO military officers make contact with their Yugoslav peers. "The day and the hour of their arrival in Belgrade should be the day and the hour when the bombing stops," said his spokesman, Valentin Sergeyev.

In addition, NATO and Russia must reconcile remaining differences about the composition and command structure of the international military force that will enter Kosovo, talks that have already been dragging on for several weeks and must now be finished in days. Beyond that, a U.N. Security Council resolution must be adopted, endorsing the agreement and spelling out the mission of the NATO-led security force and the interim civilian administration that are to take control of Kosovo.

That could happen as soon as this weekend, said some U.S. officials, although others said it could take several days longer and could still be the subject of diplomatic wrangling. U.S. officials said that despite recent strains with Beijing, they do not expect China to veto the resolution now that Belgrade has accepted NATO's terms.

Another pressing issue is how to deal with Kosovo's ethnic Albanian refugees, who yesterday were already clamoring to begin returning from camps in neighboring Macedonia and Albania to the devastated province where poisoned wells, destroyed homes and land mines await them. U.S. officials said they hope to persuade most of the 700,000 refugees in the camps to remain where they are until relief officials can deal with an equal number of internally displaced Kosovo Albanians who have been wandering the province without aid or shelter for months.

Two crucial questions that were not addressed in yesterday's agreement remain to be answered: the future of Milosevic and the status of the ethnic Albanian rebel force known as the Kosovo Liberation Army.

The KLA has been fighting for independence for the province, whose ethnic Albanians constituted 90 percent of the 1.8 million inhabitants before the conflict erupted. But NATO and the United States have rejected that goal. Yesterday's agreement provides for the province to remain under nominal Yugoslav sovereignty, with local self-government under United Nations supervision.

Secretary of State Madeleine K. Albright said she has been in regular contact with the rebel leadership. "It is our expectation that they will demilitarize," as called for in an earlier peace agreement that the rebels accepted but Milosevic did not, she said. But it remained unclear whether the KLA will still go along; it has been recruiting heavily in refugee camps and building up its following.

The status of Milosevic and other prominent Yugoslav government figures as indicted war criminals, wanted by the war crimes tribunal and subject to arrest, also could complicate negotiations over Kosovo's political future.

"It will be interesting in terms of implementation to see whether he will spring surprises regarding his own well being and the tribunal," said a senior U.S. official, who said he worried that Milosevic might seek immunity from tribunal charges before fully implementing the agreement.

Prominent members of Congress, including Senate Foreign Relations Committee Chairman Jesse Helms (R-N.C.), said they will oppose any arrangement to use U.S. troops as part of a force that would guarantee Yugoslav sovereignty over Kosovo so long as Milosevic is in office.

That sort of anxiety pervaded comments by American and European officials, who greeted news of the peace accord from Belgrade with a mixture of relief and suspicion and an impulse to mistrust and verify any commitments made by Milosevic.

"I think the English have a very good saying that the proof of the pudding is in eating it. And the same goes for peace processes," said Ahtisaari, who met with Milosevic in Belgrade yesterday morning to go over NATO's terms for ending the war.

"Our watchword of the day is caution, codification and implementation," said Rubin. The reason, said another high-ranking department official, is that when it came to earlier agreements with Milosevic, "he lied."