American Embassy officials here won't know for sure until Monday, but it's likely that a major blaze that ripped through the roof and top floor of a neighboring Soviet apartment building late Friday and early today will end the microwave bombardment of the U.S. mission that had originated from the heavily damaged structure.

Electronic devices located on or in the apartment building had been one of two sources of the microwaves beamed at the embassy in recent years, although the Soviet bombardment program goes back 18 years and has involved other sources as well.

U.S. officials have suggested that the beams are intended to trigger Soviet eavesdropping devices hidden in the embassy building. Soviet sources have said the microwaves are intended only to jam American listening devices, and a 1972 State Department report recently made public referred to the Soviet equipment as a "microwave jammer."

Embassy officials said there were no beams coming from the damaged apartment building today, but added that the Soviet bombardment normally occurs only during regular business hours, from 8 a.m. to 6 p.m. Monday through Friday. Thus, they said, they won't know for sure if the fire has damaged or destroyed the microwave equipment until Monday morning.

Other sources noted that the fire was centered on the area of the ninestory apartment building from which the microwaves have been beamed.

The building is located across a 12-lane section of Moscow's "Ring Road" from the American Embassy.

Scores of Soviet firemen and at least 20 pieces of firefighting equipment battled the blaze for about three hours in 5 degree temperatures late Friday night and early today. Flames shot 25 feet in the air from some sections of the roof and were clearly visible in at least two ninth-floor apartments.

As seen from an embassy office today, the roof of the apartment house was a charred shambles, and there was evidence of smoke and water damage on at least three floors.

"The betting is that on Monday the microwaves won't be coming on again," commented one Western diplomat.

Soviet officials refused to say whether anyone had been injured in the blaze. Surprisingly, the building was not evacuated even during the worst of the fire. Tenants were clearly visible in some apartments as high as the eighth floor.

The State Department has protested repeatedly to Soviet officials over the years that the microwave beams should be stopped. The Soviet electronic bombardment program is known in American government circles by the code name MUTS, and it has been the focus of a major controversy over the possible impact of radiation from the beams on the health of U.S. personnel here.

Aluminum screening installed at the embassy nearly three years ago reportedly has been effective in blocking some of the radiation that comes from the searchlight-like microwave beams, but it is unknown how effective they are in frustrating the eavesdropping, or countereavesdropping, program.

The Soviets have scaled down the extent of the microwave bombardment in recent years. The microwaves reportedly reached an intensity of 18 microwatts per square centimeter as recently as late 1975, several months after their existence was first publicized. Lately they have been "consistently below two microwatts per square centimeter," according to embassy sources.

A second source of microwaves is believed to be located in a Soviet building to the west of the embassy.

A similar fire 17 months ago did about $5 million in damage to the top floors of the American Embassy.