Shortly after 9 a.m. yesterday, while Washingtonians digested the news of the aborted hostage rescue attempt, a group of government employes sat in their office across from the White House, sipping coffee and munching danish pastry.

Suddenly a nearby portable radio crackled with an urgent message: "The United States is under attack! This is not a test. The United States is under attack!" The announcement, over WPFW-FM, was accompanied by the sound of wailing sirens and honking cars from the radio speaker.

Panic-stricken, 12 of the workers stumbled down to the basement bomb shelter while three others -- all employed at the federal volunteer agency ACTION -- frantically flipped the radio dial for more information.

"My first thought was "This is it,'" said ACTION information officer Les Wexler. "It sounded extremely realistic. Everyone turned 10 shades paler."

Thinking it might be a gag, Wexler flipped the radio dial, heard, disco music, then turned back to WPFW "where they were talking about nuclear fallout in Charlottesville."

"Everyone else ran down to the basement," recalled Mark Walker, who said the announcement "numbed" him. "I ran up to the ninth floor to spend the last seconds with a few close friends. I looked out the window waiting to see the mushroom cloud over Washington."

Not wanting to panic the rest of the employes, Walker simply told them he had heard a "very strange thing." No one seemed to respond, so Walker found another radio, flipped it on and discovered the nuclear nightmare was not real.

"I heard that traffic was fine on Key Bridge, two window washers were trapped and there was a sale on at Sears" he said. "I figured it was a misunderstanding. I felt rather foolish."

What Walker and the rest of the ACTION employes had heard over the Washington radio station was part of a taped dramatization of the effects of nuclear war, designed to promote antinuclear demonstrations set for today in the nation's capital.

WPFW, 89.3 megahertz on the FM dial, is one of five radion stations owned by the California-based Pacific Broadcasting Co. Its noncommercial and often controversial stations, with roots in Berkeley, Calif., are known for what the chain calls "alternative" programming.

"I think they turned in right at the worst part," said WPFW programmer David Selvin. "In fact, it had occurred to me that people might think it was real, especially because of what happened in the Iranian desert. But I try to give my audience more credit than they deserve. It was obviously a dramatization."

Selvin said the 19-minute program began at 9 a.m. with a disclaimer, and that it ended with listeners phoning in questions. "There were other people who were scared too," he said.

Several angry ACTION employes telephoined the Federal Communications Commission yesterday to lodge their complaints about the airing of the broadcast. A spokesman for the FCC said the agency was aware of the complaints, but that no decision had been made whether to investigate the incident.

"I'd shut them [the station] down today," said Peter Bender, an Action ACTION employe who called the broadcast "totally outrageous and inappropriate."

"The anxiety level in this town is right up there. We vacated that room immediately. We were in total shock. My first thought was that I didn't even have time to call my wife and children. I thought it was all over," Bender said.

"It was extremely bad timing," said Wexler, recalling the panic that Orson Welles set off in 1938 with his "War of The Worlds" radio broadcast. o"I had waked up in the middle of the night, and had been listening to the Iranian crisis. It was a very tense time."

Beverly Litner, another ACTION employe, said the broadcast "was in very poor taste. People started to cry and say, 'My babies are in school.' Not that we felt rescuing the hostages would cause an attack on us, but you react before you think."

Litner said she immediately called the radio station and spoke with the receptionist. "She [the receptionist] laughed and said, 'Yeah, I wondered what would happen if people thought it was true.' I said, 'you better get on the air and tell the announcer it's freaking people out, especially because of Iran."

Station manager Loren Cress Love said yesterday the nuclear dramatization had been shelved. "We're certainly not going to be playing it again," she said.