U.S. Jets Bomb Bosnian Serb Positions at Muslim Enclave : Balkans: Direct hits are reported on a command center and a tank position outside Gorazde. Rebel shelling is halted, observers say. It is unclear if artillery units have begun a pullback.

Two U.S. jet fighters bombed Bosnian Serb artillery positions outside the eastern enclave of Gorazde on Sunday, halting a fierce rebel offensive in its tracks and delivering the first punishing air strikes after months of U.N. threats.

Launched by NATO, the bombing run was the alliance’s first-ever air attack on ground positions. It came more than three hours after a final U.N. warning to the Bosnian Serb military chief that demanded an immediate end to the current offensive, which has claimed more than 100 lives in the enclave over the last two weeks.

On Sunday, the United Nations said that the rebel shelling had suddenly put the lives of its peacekeepers and other personnel at “direct risk.”

U.S. Defense Secretary William J. Perry said two F-16C warplanes took off from Aviano Air Base in northern Italy. They dropped a total of three 500-pound bombs under the direction of a U.N. forward air controller.

Bosnian Prime Minister Haris Silajdzic claimed that the air attacks scored direct hits. U.N. sources said a command post and a tank position were bombed.

Serbian shelling of the mostly Muslim enclave of Gorazde, one of six U.N.-designated safe areas in war-torn Bosnia-Herzegovina, ceased two hours later, said Michael Williams, spokesman for the U.N. Protection Force, quoting reports from U.N. military observers in the town.

It was not immediately known whether the Serbian forces that have harassed Gorazde with tank and mortar fire had begun withdrawing from territory seized in the offensive, as demanded by the U.N. commander for Bosnia, British Lt. Gen. Michael Rose.

President Clinton, expressing the hope that the limited military operation would bring the Bosnian Serbs to a peace conference, emphasized that the international community is united in its resolve.

“This is a clear expression of the will of NATO and the will of the United Nations,” he said in a brief statement and question-and-answer session with reporters on the White House grounds. “We were retaliating. The United Nations made it absolutely clear that there were U.N. personnel in Gorazde, that an attack on the town would be interpreted as a clear violation of the rules.”

Word of the air strikes was released only after nightfall, but the Bosnian government expressed confidence that the use of force would have the desired effect of driving the rebels back.

“We know their reaction. They are bullies. They react to force,” Silajdzic told reporters shortly after news of the attack, thanking the United Nations and the North Atlantic Treaty Organization for coming to the defense of his country.

“We must express our gratitude to all those who helped the resistance of Bosnia-Herzegovina to fascism. That is psychologically very important for our people who have suffered for almost two years,” the prime minister said.

“There are 16,000 killed children--16,000 killed children! That is 1,600 playful schoolyards swept off this earth,” he said. “I think these people of Bosnia-Herzegovina are entitled to relief, to know we are not alone. It is very, very important for our people to know that the genocide is going to be punished after all.”

Bosnian Serbs accused NATO of hitting civilian targets.

“With this action NATO has committed open aggression against the Serb people by attacking civilian targets far from the front,” a Bosnian Serb statement said.

Gen. Milan Gvero, deputy commander of the Bosnian Serb army, said there were civilian casualties but did not elaborate, according to the Bosnian Serb news agency SRNA.

The air strike was the first of its kind in NATO’s 45-year history. The only other use of NATO air power in the more than 2-year-old Bosnian war came Feb. 28, when NATO jets downed four Serbian planes in central Bosnia after the aircraft violated a “no fly” zone. Also in February, the threat of air strikes forced Bosnian Serbs to withdraw their guns from Sarajevo.

Sunday’s strike was ordered after Rose informed the U.N. force commander for the former Yugoslav republics, French Gen. Bertrand de Lapresle, that the Serbs were firing on the center of Gorazde with tanks that had penetrated the heavily populated southern suburbs of the city.

“Aside from the increased risk to civilian lives, the lives of UNMOs (U.N. military observers) in the town, as well as of other U.N. and its humanitarian personnel, were assessed to be in direct risk,” Williams said in describing the decisions that led to the air strikes.

Rose then asked Lapresle to request close air support from the civilian chief of the U.N. mission, Yasushi Akashi, who is the special representative of U.N. Secretary General Boutros Boutros-Ghali.

Unlike the only other time U.N. commanders asked for air power to back up operations on the ground, the request was granted in 25 minutes, according to Williams.

A U.N. appeal in March for NATO air cover took more than three hours to be approved. In that time, the Bosnian Serb gunmen who had been attacking French U.N. troops near Bihac had time to escape retribution.

U.N. officials appeared somewhat concerned that the resort to force might undermine their already difficult quest for a cease-fire in a war in which at least 200,000 people have been killed or are missing, mostly Muslim civilians.

“We would hope the peace process is not seriously impaired,” said Williams, Akashi’s spokesman.

The Bosnian Serb leadership early today sharply protested the NATO attack and accused the United Nations of siding against the Serbs. The rebels declared that they were breaking off contacts with U.N. peacekeepers.

Rose and U.S. special envoy Charles Redman have spent the last three days shuttling between Bosnian army headquarters and a Serbian base just outside this capital in a fruitless attempt to mediate a truce.

At a news conference before the air strikes, Silajdzic and Bosnian President Alija Izetbegovic accused the Serbs of toying with the Western mediators by taking part in the negotiations while continuing the offensive.

Serbian rebels had advanced on the Gorazde enclave despite escalating warnings from the U.N. commanders that aggression would not be tolerated while a diplomatic solution was being sought.

A final warning was telephoned to the Bosnian Serb military chief, Gen. Ratko Mladic, at 2 p.m. local time Sunday, Williams said, and the same message was relayed by facsimile 50 minutes later.

There was no response from Mladic. But Gen. Manojlo Milovanovic, the rebels’ second-in-command, contended in a letter to U.N. commanders here that the Serbian military leadership had ordered a halt to attacks on Gorazde.

“We can reliably inform you that Republika Srpska (the self-styled Bosnian Serb state) mortars and artillery rounds are not falling into Gorazde,” Milovanovic insisted in the letter received by U.N. officials at 6 p.m.

However, shelling continued until 7:25 p.m., Williams confirmed.

Lapresle planned to meet today with Bosnian Serb leader Radovan Karadzic, as well as with Izetbegovic, the spokesman said.

Boutros-Ghali had raised the threat of NATO air strikes a day earlier, after Serbs captured strategic high ground around Gorazde and began shelling the refugee-packed city center.

Gorazde, Zepa and Srebrenica, which were designated U.N.-protected havens last May, are the last three areas of eastern Bosnia not yet subjected to the Serbian rebel scourge of “ethnic cleansing.”

Gorazde is important for the Serbs because it sits astride the main highway linking their territories in southwestern and eastern Bosnia. Its continued control by government troops forces Serbs to depend on roads through Yugoslavia or mountain routes south of Sarajevo.

International aid workers had reported earlier Sunday that Serbian shelling of Gorazde had triggered panic and that thousands were fleeing the eastern bank of the Drina River as the rebel tanks rolled in.

A spokesman for the Office of the U.N. High Commissioner for Refugees, Peter Kessler, said 5,000 refugees had fled their homes in the Gorazde pocket, most within the previous 24 hours.