The bright red flag of the Soviet Union flew at half-mast at that nation's ornate embassy on 16th Street NW yesterday, as somber-faced officials, wearing red armbands bordered in black, greeted members of Washington's diplomatic corps.

The diplomats, representing every corner of the world from Nepal to the Netherlands, Uganda to Nicaragua, had come to offer official condolences to their Soviet counterparts on the occasion of the death of Leonid Brezhnev.

Once inside the embassy, the diplomats were led up a winding marble staircase to a dimly lit room on the second floor where a huge portrait of the late Communist Party leader, edged in black, stared down over a large display of red roses and the red leather chair and wooden desk where the diplomats sat to record their condolences in a thick, leather-bound book.

Soviet officials, some in olive-green military uniforms, stood against the walls, where mirrors had also been bordered in black, and watched silently. Most of the diplomats merely wrote "With sympathy," then signed their names.

Secretary of State George Shultz was among the first to arrive, shortly before 9:30 a.m. He stayed about 10 minutes, then left accompanied by Soviet ambassador Anatoliy F. Dobrynin, who gave him a farewell handshake. Like most of the other diplomats, Shultz left without commenting to the cluster of reporters gathered outside.

The non-Soviet press was prevented from filming or photographing the room set up in Brezhnev's memory while the diplomats were there because, the embassy press attache explained, exclusive rights to those scenes were promised to Soviet television.

There was also an unusual amount of activity at the embassy on Thursday, when news of Brezhnev's death of a heart attack spread across the world. Soviet officials who work at the various offices the Soviets have throughout the city streamed in and out of the main embassy building throughout the day, though none would comment on Brezhnev's death to reporters waiting outside.

"Since this is such a sad occassion, everybody tended to want to be together. It's quite natural," a spokesman for the embassy said. The spokesman said the officials observed a moment of silence in Brezhnev's memory.

There were the usual small protests at the embassy yesterday. A sign hung from the building across the street declaring, in Polish, "Solidarity." And as has been the case for the past 12 years, members of the Jewish Community Council of Greater Washington gathered in front of the embassy at 12:30 p.m. to pass out leaflets decrying the treatment of Soviet Jews and dissidents. Theirs is one of the longest-running protests in Washington.

At the school for the children of Soviet diplomats, part of the Soviet complex on Tunlaw Road NW, classes were in session Thursday and yesterday but there will be no classes for the children on Monday, when Brezhnev is to be buried, according to a spokesman.