Effie Barry, wife of Mayor-elect Marion Barry, gave her first public party last night, a rousing disco dance in celebration of Kwanza, the Afro-American celebration of traditional African harvest festivals.

She set a tone of informality and grace in her social debut as the city's first lady, moving with ease through the crowd of 200 people at the Last Hurrah discotheque.

Mrs. Barry, 34, unhesitantly introduced herself to couples in the middle of some heated versions of the latest dance, "The Rock."

"I thought this party would be in keeping with the serious way Marion and I have celebrated the holiday season. Kwanza ends on Jan. 1, also, and our administration starts on the second. And the administration will emphasize many of the principles of Kwanza -- creativity, purpose and unity," she said.

A native of Toledo, Ohio, Effie Barry has used her degrees (Hampton Institute and City College of New York) in home economics and health education to work as a teacher, an airline stewardess and an analyst for Dun and Bradstreet.

Since she moved to Washington three years ago, she has worked as a specialist with the local environmental health administration. A tall, thin woman with ramrod posture and expressive gestures, she intends to work closely with senior citizens' and children's groups during her husband's administration.

On the invitation for last night's celebration, Effie Barry had requested that guests bring new or old toys. As she peeked into a shopping bag, she periodically clasped a teddy bear or rag doll to her chest. At one point a bartender of the club interrupted her, saying, "I think it's wonderful that you're doing this."

Some of the guests did not know Mrs. Barry personally but like Angela Edwards, a management consultant, thought the idea of collecting toys for youngsters was a good idea.

Among the crowd were D.C. fire chief Jefferson Lewis, attorney Herbert Reid and George Sealey, a protocol officer at the State Department. Sealey, who has been meeting with Effie Barry on protocol issues, said, "She is first rate, very poised and is looking for new ways to interface with the international community. I think it will be a new Washington with her.'

At midnight Mrs. Barry was joined by her husband in lighting a black candle to honor the start of the fourth day of Kwanza. The day commemorates the principle of ujima (collective work and responsibility). After Mrs. Barry explained the relationship of the celebration to the goals of the new administration, Amina Dickerson of the Museum of African Art explained in detail the celebration.

Then the jam session resumed.