U.S. Leaders Get Pentagon Briefing on Military Options to Halt Serbs’ Advance : Balkans: Advisers focus on air strikes on artillery positions. Plan could require U.S. ground forces.

Pentagon war planners, responding to mounting frustration on the part of the Clinton Administration, have briefed U.S. leaders on a broad range of military strike options designed to blunt the Serbian-backed advance into Bosnia-Herzegovina and to loosen the Serbs’ grip on besieged towns and cities like Sarajevo.

As the crisis in eastern Bosnia worsened, Clinton’s key national security advisers focused on one of the narrowest and, in one official’s words, “most benign” of the military options--use of U.S. and possibly allied aircraft to strike Serbian artillery positions. And by doing so, officials said they have confronted fears and challenges, including the possibility that even the most limited air strike could require introduction of some U.S. ground forces into Bosnia.

For Clinton, who as recently as Friday said that he has “never ruled in” the use of U.S. ground troops in the conflict, that fact could pose political difficulties. But so do the alternative plans drafted by Pentagon planners, officials said. Those plans include sweeping strikes on Serbian supply routes into Bosnia and on major structures inside Serbia whose destruction could force recalcitrant Serbian leaders to the peace table.

On Sunday, Clinton and Prime Minister John Major of Britain welcomed the U.N. Security Council’s vote late Saturday to tighten existing sanctions against Yugoslavia, which now consists only of Serbia and Montenegro. Among other things, the new measures, effective April 26, would freeze all of Serbia’s overseas assets.

Clinton and Major talked for nearly an hour on the telephone, the White House announced, and discussed “other options” in the Bosnian crisis.

Pentagon contingency plans for the former Yugoslav federation have long been drafted and often been rejected, most vocally by military leaders themselves. Led by Gen. Colin L. Powell, chairman of the Joint Chiefs of Staff, military leaders have repeatedly raised questions about the risks, the costs and the effectiveness of U.S. intervention.

From their first days in office, when Clinton Administration officials were presented with the Pentagon’s war plans, they have been stymied by the military’s portrayal of Bosnia as a dangerous and messy sinkhole that could draw in U.S. forces and make their exit difficult.

American military leaders as late as last week remained unenthusiastic about the prospect of using even limited U.S. force to aid Bosnia. The commander of all American and alliance forces in Europe, U.S. Army Gen. John M. Shalikashvili, pointedly warned that outside forces would face difficult dilemmas if they were to intervene to stop Serbian aggression.

At the same time, however, many senior military officers--including several who work for Powell--have acknowledged that the deft use of American air power could drive Serbian-backed forces into more defensive positions and help muffle--if not silence--Serbian artillery.

Knowledgeable sources said that plans to strike at Serbian artillery emplacements would likely involve massive use of high-tech, precision-guided munitions and limited use of U.S. commandos on the ground, armed with targeting beacons, laser designators and night-vision equipment.

Intelligence would be key to the success of such an operation, military sources said. American pilots would need to know precise locations of artillery pieces, gathered from aerial and satellite photography and from commandos equipped with special radar.

Commandos also could be covertly moved by helicopter into areas from which they would spread out and plant special targeting beacons--as they did in Iraq during the Persian Gulf War--near Serbian weapons caches.

Specially equipped American warplanes--Air Force F-15E Eagles and F-111s flying out of Italy and Navy F/A-18 Hornets flying from aircraft carriers in the Adriatic Sea--could then hit Serbian weapons with missiles and bombs and home in on their targets with laser beams, heat-seeking devices or other electronic devices.

While such strikes could not put an end to Serbian artillery and mortar attacks, military experts said that, for the first time in the year-old war, they could harass and endanger Serbian-backed gunners who have brazenly camped in the hills surrounding Muslim towns and conducted nonstop bombardments against civilian populations.

As soon as they fired, Serbian weapons would reveal their locations and the Serbian gunners would be threatened with destruction. So such an air campaign could keep Serbian gunners on the run and make their attacks more sporadic and possibly less deadly.

“You’re raising the cost for them to continue their behavior,” said retired Air Force Gen. Michael Dugan, a former Air Force chief of staff who has argued that the United States should launch an air campaign to help the Bosnians.

“It’s certainly doable,” Dugan said. “We have the equipment and trained crews and technology and the weapons. . . . It’s a policy question: Do we want to do it, and how much risk are we willing to accept, and who else will join us?”

Pentagon officials have said, however, that the mobility of Serbian mortar and artillery pieces would make such an operation difficult and limit its effectiveness. In addition, Shalikashvili warned Friday that, even with high-tech advantages, U.S. forces would be plagued by the possibility of causing civilian casualties.

“No one these days installs artillery in woods where they can easily be taken out without collateral damage. Now there is artillery in villages and residential areas,” Shalikashvili told the Belgian newspaper De Standaard in an interview published Saturday. “If you bombard those, you must also be prepared to see pictures on CNN of children and women and men being killed.”

The dangers and limitations of such an operation have led some experts and officials here to favor air strikes against supply lines from Serbia.

“If you want to get to the heart of the problem, you have to go somewhere else”--beyond the artillery pieces surrounding Muslim towns, Dugan said in an interview with The Times.