MOSCOW, MARCH 1 -- A three-minute demonstration of the limits of glasnost was played out today on the steps of the Lenin Library.

At noon, eight Crimean Tatars unfurled banners demanding that their people -- whom Joseph Stalin had deported to reservations in Central Asia in 1944 -- be allowed to return to their homeland near the Black Sea. Within moments, uniformed militia and plainclothed KGB agents seized the signs and hauled the group to a station.

"You just saw a little bit of glasnost in action," said Alexander Podrabinek, an editor of the underground weekly Express-Khronika, who has been jailed twice for dissident activity. "Everybody in the papers talks about openness and democratization but, in life, what do we have?"

Podrabinek was in Red Square last July when hundreds of Tatars brought their case to the Kremlin. Today's demonstration was the first by the ethnic group since then. Last August, the Moscow city government began requiring authorization of any demonstrations. The Tatars, even in so small a group, knew their protest could last only a few moments.

Half an hour before the demonstration was to begin, agents arrived. Some talked into their lapel microphones. Others panned the area with Japanese video cameras. Others snapped still photographs.

Usually demonstrators in Moscow contact at least a few foreign correspondents ahead of time. Then the protest begins, the police stop it, and the reporters write their stories.

Today, the demonstrators had not alerted correspondents and it was only by chance that this reporter noticed. Yuri Kislyov, who lost his legs in World War II and 10 years ago organized the Initiative Group for the Defense of the Rights of Invalids in the U.S.S.R., came to the protest and met his friend Podrabinek, the editor.

As soon as the agents caught sight of the two talking with a reporter, four KGB men encircled them and tried to interrupt. One agent kept trying to read the reporter's notes.

"Why are you writing?" the agent asked. "Why are you listening to these people? What do they have to say?"

Every time Podrabinek tried to lower his voice and speak to the reporter, an agent would dip his head into hearing range, as if his intention was to intimidate as well as to listen.

"Would you like me to speak a bit louder for your microphone?" Podrabinek asked. The agent did not smile.

"You are anti-Soviet, aren't you?" one agent asked Kislyov.

Kislyov, who wheels himself around Moscow on a foot-square cart just inches above the ground, did smile. A circle of people looked down at him, waiting for his reply.

"It's you who are anti-Soviet," he said. Kislyov added that Lavrenti Beria, Stalin's secret police chief, was anti-Soviet as well.

There was a long silence. Then an agent pointed to the Crimean Tatars who were taking their place on the top of the steps. "Why do you bother with them?" the agent asked. "It's their problem, not yours." Neither Kislyov nor Podrabinek is Tatar, but they came to support the demonstration and, in Podrabinek's case, to write about it.

As soon as the Tatars unrolled their banners, agents and uniformed militia descended on the group. Two busloads of agents emptied onto the square in front of the library. Their cameras whirred.

The officer in charge asked questions but the protesters fixed their eyes above his head and said nothing. With that, the police grabbed them by the elbows and led them away.

The police took the names of Podrabinek, Kislyov and the reporter, and one agent continued to follow the three of us as we searched for a spot to hail a taxi. The agent broke into a smile whenever Kislyov looked over his shoulder.

The agent caught up near the Arbat metro station and said, "You might have better luck getting a cab on the other side of the street."

"The KGB wants us to think that they are just people with a job to do," Kislyov said.

"From my point of view, glasnost has a frame around it," Podrabinek said. "There is a euphoria about it in the West, but I think really the government is just trying to win prestige in the West for economic purposes, for trade, maybe. Unless they allow some kind of legalized opposition here, until there is a guaranteed political mechanism for opposition, we've got nothing."

Four hours after the demonstration began, Kislyov said the eight protesters had been released and sent back to the Crimea and Tashkent.

This summer, the Soviet government formed a special committee to deal with the Tatar issue. The committee has not yet announced its conclusions.