Facing a sea of black faces and urged on by frequent applause and shouts of "amen" and "right on," Mayor Marion Barry talked like a tough black community activist yesterday, telling a gathering of government employes that discrimination is "rampant" in the nation and its capital city.

For the mayor, whose aides have advised him to be "more mayoral" since becoming chief executive of the nation's capital, speaking at a Black History Week observance sponsored by the General Services Administration offered a chance to return to the pointed rhetoric from the days of black activism that made Barry well-known in this city a decade ago.

He talked about the horrors of slavery, ticked off names and important dates in black history and driven on by the enthusiastic response of his audience, he preached, it seemed. Breaking from his usual protocol of being nice to his host, Barry even made GSA the target of some of his criticism.

"The struggle is not over. There is still rampant discrimination in America. There is still discrimination in Region III of GSA," he said.

Jackie Council, a 12-year GSA employe, said "amen" to that, even though she has a job with the federal government -- the kind of job that has long been coveted in black communities throughout the country because of the security it usually offers.

"Yeah, it gives me security. But it doesn't give me a future to keep up with the rising costs of living," said Council, who lives in the Fort Dupont area of Southeast Washington.

"Did you see any blacks when the heads stood up?" she said referring to the introduction at the beginning of the program of eight top GSA regional officials, all of whom were white.

Grady Heflin, 53, a GSA mail branch employe who lives in Hillcrest Heights, indicated that he could also identify Barry's assertion of bias in GSA and was glad the mayor said what he did."

"It's secure here, but they keep you on the bottom," Heflin said. "Some of those same people who are holding me back were sitting up there in the front seats.

"I think they got the message this time. The mayor can say it and get away with it. I probably couldn't."

Yesterday's activities at the GSA regional headquarters building in Southwest Washington marked the second year in a row that the agency has held a Black History Week program.

"It's more or less a form of exhaust, you feel good letting someone know there are problems that have to be resolved," said Eugene Waller, director of equal employment opportunity for the agency. "We have a Spanish Heritage Week, we have a Federal Women's Week. Why not a Black History Week?"

Several GSA employes interviewed yesterday said Black History Week offered them an opportunity to come together and, in the unity of numbers, say aloud what was often only whispered during office lunch breaks, on buses and in car pools on the way home.

Barry, who frequently speaks stiffly and in language laced with bureaucratic jargon, had a chance yesterday to use the abundant black history and activist phraseology that he had stored up during several years as a radical black community activist before becoming involved in politics.

The mayor talked about divisions between different kinds of blacks during slavery and also declared at one point, "whether you are a PhD. or a no D, if you're black in America you're gonna catch hell."

He poked fun at his audiance. "I grew up in the South. A lot of y'all did too, but you don't want to admit it right now," he said at one point.

The mayor criticized the local daily newspapers, saying they were overly critical of him because he is black. "The Washington Post and the Washington Star expect me to be five times as good as a white mayor ought to be with five times less resources.

"Full equality will come when we can have an incompetent and nobody worries about it anymore than when they have an incompetent white mayor."