Clouds Hamper U.S. Planes in Attack on Serb Tanks at Gorazde : Balkans: Some aircraft forced to hit alternative targets. Action shows difficulty facing NATO.

It was in the cloud-enveloped, sunless mountains around Gorazde, Bosnia-Herzegovina, this past weekend that one of the reasons for the Western allies’ long reluctance to launch air strikes in the Balkans became crystal clear.

The pilots of the two U.S. Marine Corps F/A-18s came in low Monday, according to the after-action reports--but they still could not pinpoint all the Bosnian Serb tanks that they had been directed to silence. Instead, they destroyed just one tank.

On Sunday, in similar weather conditions, made worse by the rugged terrain, two U.S. Air Force F-16s had been forced to pass up a cluster of tanks and pick an alternative target. Their “kill” that day: one Bosnian Serb command tent and a few trucks.

Although the Clinton Administration is not emphasizing the point, military analysts said the air action in Bosnia already is demonstrating the difficulty that North Atlantic Treaty Organization aircraft will have in effectively halting a Serbian advance on the town if the Serbs prove intent on continuing one.

In contrast to the cloudless nights and open lines of sight that allowed U.S. pilots a field day in the Persian Gulf War, the Balkans are a treacherous combination of mountainous terrain and frequent poor weather. And the Serbs are scattered, not massed as the Iraqi troops were.

Gorazde itself is in a valley, almost buried by steep mountains on every side. The Drina River runs to the south and east, with the city, like an elongated pear, pushing north from the water. There is high ground on the river’s southern bank.

Despite all the shooting, neither side has tremendous numbers of ground troops in the area. The Muslims have about 6,500 soldiers inside Gorazde, supported by a handful of tanks. The Serbs have 4,500 men in the area, with larger numbers of tanks and artillery.

It was from high ground that the Bosnian Serb tanks began their shelling Sunday. Two of them lobbed shells into the city, guided by fire-control observers in a command post on a mountainside about 500 feet above. The air was misty, the cloud cover low.

The United Nations had sent an 11-man contingent to Gorazde to serve as military observers in the area, and the Serbian tank fire was getting too close. By midafternoon, the U.N. mission had radioed for close-air support and the request had been approved by the chain of command.

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At 3 p.m., the two U.S. F/A-18s responded but were unable to pinpoint the target, despite two high-speed warning flights. They lost communication with their ground controllers. Low on fuel, and with the weather deteriorating by the minute, they turned back.

NATO then sent in two U.S. Air Force F-16s, but they too ran into trouble--partly because of the weather and partly because the British unit that had been dispatched to direct the bombing from the ground did not have the necessary laser equipment.

Unwilling to let them return to base empty-handed, NATO ordered the F-16 pilots to attack the command post instead. With a few notable exceptions, the Serbs were quiet through the night.

But Monday, the Serbian barrage resumed, and two more F/A-18s responded to the call for help, trying to strike back against tanks and armored personnel carriers. But the pilots had difficulty finding targets under the cloud cover.

The result was unsatisfying. “It’s a law of physics,” Marine Corps Lt. Gen. John Sheehan, operations officer for the Joint Chiefs of Staff, told reporters later. “Flying in bad weather, regardless of the technology of the machine, is hard.”

Military analysts said that the strategy is a high-risk gamble. If the West can persuade the Serbs to press for peace by expending a few bombs to make a point, then this past weekend’s operations, largely symbolic, will prove effective.

But if the Serbs hold firm, the West could be in for a messy, protracted affair. “What this tells us is that we’re in the deep end of the pool,” said a former Air Force officer who has been keeping tabs on the operation. “I think we’re going to lose some airplanes soon.”