NATO Halts Bombings in Bosnia : Balkans: Air strikes are suspended for three days. Attacks to resume if Serbs fail to pull heavy weapons away from Sarajevo.

NATO halted its aerial bombardment of Bosnian Serb positions Thursday after the rebels agreed to begin lifting the 41-month siege of Sarajevo.

The Bosnian Serbs said they were willing to withdraw some of their heavy guns from around this devastated capital in exchange for an end to North Atlantic Treaty Organization air strikes and a requirement that Bosnian government forces register their heavy weapons with the United Nations.

Air strikes will be suspended for three days and will resume if the Serbs fail to withdraw their weapons from a 12 1/2-mile exclusion zone around Sarajevo, the United Nations said in a statement Thursday night.

During the hiatus, humanitarian aid convoys will be allowed to travel to the Bosnian capital on two roads through Serb territory that have been closed, and it is expected that Sarajevo airport will be reopened without restrictions, the United Nations said.

As described, the agreement falls short of the unconditional removal of Serb weapons that NATO had, until now, insisted upon. But if it works, it would reduce the threat to Sarajevo and break an impasse that grew as NATO repeatedly demanded removal of the weapons and Bosnian Serb army commander Gen. Ratko Mladic steadfastly refused. The impasse jeopardized larger efforts to resolve Europe’s deadliest conflict since World War II.

With the air campaign launched 16 days ago, NATO embarked on the largest combat operation in its history to dislodge the Serbian weaponry that has menaced Sarajevo for nearly 3 1/2 years.

In Washington, President Clinton expressed optimism that a Balkan peace is finally within sight.

“There’s been some reason to hope for progress in the last several hours,” Clinton told reporters at the White House. “We are working on the details of an agreement.”

But others cautioned that the Serbs have reneged on agreements in the past. Three days into the aerial campaign, NATO suspended the bombing to give Mladic time to comply with alliance demands. Facing an ultimatum, the Serbs moved weapons around to give the appearance of a withdrawal, but it turned out to be a ruse, U.N. officials say. Bombing resumed.

The new agreement first emerged in an 11-hour meeting in Belgrade, capital of the rump Yugoslavia, on Wednesday between Serbian President Slobodan Milosevic and U.S. envoy Richard Holbrooke, shepherd of a U.S. diplomatic initiative that is aimed at ending the bloodshed in the former Yugoslav federation.

Milosevic told Holbrooke that the Bosnian Serbs were finally prepared to comply with NATO demands. Then, with dramatic flair, Milosevic backed up the offer by abruptly ushering Mladic and Bosnian Serb leader Radovan Karadzic into the meeting with Holbrooke.

It was the first meeting between such a senior U.S. official and Karadzic and Mladic, both of whom have been indicted for war crimes.

State Department spokesman Nicholas Burns said Holbrooke had expected little more than a preliminary discussion of peace proposals when he began the marathon session with Milosevic. However, Burns said Milosevic unveiled a detailed peace plan calling for the Bosnian Serbs to pull their heavy weapons back from Sarajevo.

Holbrooke dashed from the Belgrade meeting to Zagreb, the Croatian capital, and then to the central Bosnian city of Mostar, where he briefed Bosnian President Alija Izetbegovic on Thursday.

While Clinton Administration officials in Washington were celebrating the agreement as all but a done deal, there were signs here that the Muslim-led government of Bosnia was less than pleased.

Izetbegovic emerged grim-faced from his meeting with Holbrooke. The two issued perfunctory statements and said talks would resume today. “We repeated our request for the lifting of the siege of Sarajevo, and Mr. Holbrooke supported our idea that Sarajevo must remain unified,” Izetbegovic said.

The president and Holbrooke met in Mostar, a city divided and badly damaged by an earlier war between Bosnian Muslims and Croats. The two groups more recently have forged a tenuous alliance that in the past month has scored important battle victories over the Serbs, once seemingly invincible.

Holbrooke will travel today to Geneva for talks with representatives of the five-nation Contact Group of mediators. He had abruptly postponed the meeting, first scheduled for Thursday, to pursue the Milosevic pledge.

“We think we made some progress today in regard to the situation in Sarajevo,” Holbrooke said after the Milosevic session.

Under the agreement, NATO reportedly gave the Serbs 72 hours, starting Thursday night, to begin withdrawing the estimated 300 mortars and artillery pieces that they hold in the hills around Sarajevo. If in that period there are concrete indications that the pullback has begun, the Serbs will be given another 72 hours to finish the task.

After that, the air campaign will end, provided the Serbs remain in compliance.

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NATO spokesman Jamie Shea said that, for the pause to be extended, the U.N. commander in the Balkans, French Gen. Bernard Janvier and NATO’s southern area commander, U.S. Adm. Leighton Smith, would need written assurances from Bosnian Serb military and political leaders and evidence on the ground that the pullback had started.

“We want to see something real,” stressed a NATO official who declined to be identified by name. “We’re not talking 10 weapons in three days, we’re talking a major shift of their arsenal away from the city.”

Momcilo Krajisnik, who heads the self-styled Bosnian Serb Parliament, went on Bosnian Serb television Thursday night to laud the agreement as a victory for the Serbian people. “We have achieved an agreement to freeze the NATO bombing,” he said. “We made a big step for the normalization of life in Sarajevo.”

The agreement also requires Bosnian government forces to put their heavy weapons under U.N. supervision, though they would not have to physically move the weapons, Krajisnik said. He said the Serbs, on the other hand, will not be required to withdraw some of their lighter weaponry.

Under the deal, the United Nations and NATO will guarantee a cease-fire, followed by the opening of roads and the resumption of electricity, gas and water, Krajisnik said. As part of the siege, the Serbs have cut most utilities to the city, as well as blocked roads and forced shut the airport, ending a vital airlift of humanitarian aid.

Sarajevo has endured perhaps the longest siege in modern history. Lifting it would dramatically alter the desperate lives of Sarajevo’s estimated 300,000 people, who have remained trapped in a virtual concentration camp for 41 months.

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The city’s future remains one of the key points of contention in ongoing peace talks. The government wants to keep Sarajevo as a united capital; the Serbs want to hold on to their sections, mostly suburbs.

And in a development unthinkable only a few years ago, Russia will be invited to join a NATO-led force to police any eventual peace settlement, U.S. Defense Secretary William J. Perry said Thursday in Washington.

“It is important to invite them to participate,” Perry said, reflecting a conclusion that including the West’s former Cold War adversary would be better than leaving them carping on the sidelines. Russia has been a bitter critic of NATO’s air campaign.

But NATO and Russia have not yet discussed a possible joint peace force, U.S. officials said.

Adding Russian soldiers to a NATO force of 50,000 or more troops would produce logistic and policy headaches that could complicate what already shapes up as perhaps the most difficult task ever undertaken by the alliance.

Although the suspension of air strikes was announced late Thursday afternoon, NATO officials at the Southern Command headquarters in Naples, Italy, said no attacks had been carried out since late Wednesday. They said that officially, the strikes had been canceled because of poor weather over Bosnia.

NATO officials, who hinted for the first time Wednesday that the alliance was prepared to take some of Mladic’s security concerns seriously, stressed that they were prepared to accept that the estimated 20,000 Serbs who live in and around the Bosnian capital required protection once the weapons were removed.

Perry said he believes that the siege of Sarajevo will end soon.

“I can voice cautious optimism--and the emphasis is on optimism--that we can achieve a peace agreement in Bosnia,” Perry told a luncheon meeting of reporters. “I expect we will see a lifting of the siege of Sarajevo in the very near future.”

Perry said the Bosnian Serbs apparently are now inclined to accept a diplomatic solution because two weeks of NATO air strikes have persuaded them that a military victory is no longer possible.

He said the NATO air campaign “achieved a level of effectiveness even greater than Desert Storm,” the 1991 U.S. military operation in Iraq. At the same time, he said, NATO has succeeded in limiting collateral casualties among civilians.

“I think there have been no civilian casualties . . . and assertions to the contrary are just propaganda,” he said.

Wilkinson reported from Sarajevo and Marshall from Brussels. Times staff writer Norman Kempster in Washington contributed to this report.