"I'm going to win with all these good Democrats," Mayor Marion Barry exclaimed, his left arm sweeping toward City Council nominees David Clarke, Betty Ann Kane, Frank Smith and Hilda Mason, who stood with him on the dance floor of a downtown private club last Thursday night.

"Of course, Hilda," Barry quickly added, "even though she's not a local Democrat, she's a national Democrat. She's our friend . . . . " The overflow crowd cheered its approval.

For Mason, the spry, wiry, 66-year-old, at-large D.C. City Council member who is unopposed in her bid for reelection Tuesday, the identity oversight was routine.

It was evidence again of the personal and political acceptance she has enjoyed in this overwhelmingly Democratic city since winning a school board seat in 1971 and then moving to the council in 1977 under the banner of the tiny D.C. Statehood Party.

Her staff long ago quit trying to keep track of the numerous social and political organizations that she and her husband, Charles, have supported: a network of civil and human rights groups that has given her a reputation for compassion among her friends and for being ultraliberal among some of her opponents.

Despite her personal appeal, Mason's political success also can be attributed to a unique restriction in the city's home rule charter, designed to blunt the 8-to-1 edge D.C. Democrats have over other voters, that has the effect of prohibiting any political party from holding more than two of the council's four at-large seats.

But the city's weak GOP has yet to field a popular candidate other than veteran D.C. politician Jerry A. Moore, 66, who plays down his party affiliation and regularly sides with the Democratic majority on most social issues. No independent candidate or other political party has made a significant effort to win a seat since the city began holding council elections in 1974 with the exception of the Statehood Party, which currently has fewer than 1,500 members.

Mason breezed to the Statehood Party nomination in September without opposition, receiving a total of only 227 votes. By contrast, Democratic candidate Johnny Barnes received 13,033 votes in his attempt to unseat Kane, yet came in a distant third.

"I really don't know why I don't have any opposition," Mason said when asked about her enviable position. "I enjoyed not having to campaign hard, because I work hard."

She is planning no victory party, has done only one small campaign mailing, and no media advertisments. Today, just three days before the general election, some volunteers are scheduled to put up the first Mason campaign posters.

Her campaign, she said, has consisted of doing what she always does: keeping up an early-morning-to-late-night schedule of meetings. In particular, she has crisscrossed the city promoting the proposed statehood constitution and the nuclear freeze initiative, which appear on Tuesday's ballot.

Last spring, Mason and her husband were among 45 elected delegates to the D.C. constitutional convention that drafted the controversial document. Mason now says that, while it is flawed, voters should support it and the council and Congress later can propose amendments.

Mason was an early supporter of the nuclear freeze issue, a natural outgrowth, she says, of her longtime work in the civil rights movement and her campaigns for gun control and against the death penalty.

Mason, a former teacher and assistant principal who was elected to the school board in 1971, was appointed to the council in 1977 after Statehood Party leader Julius Hobson died. Later that year she defeated nine other candidates in a special election to serve out Hobson's term. In 1978 she won a full term.

While Mason is not known for her ability to draft legislation, she still is one of the most respected members of the 13-member council, assuming, in her dignified and motherly tones, the role of the council's liberal conscience on social issues.

A strong proponent of such issues as rent control, life tenancy for the elderly, and a pending "repair and deduct" bill that would allow tenants to use rent monies for repairs, Mason has drawn sustained criticism from the city's real estate interests.

"All of her thrust seems to take the consumer interest," one representative of real estate interests here said. "Certainly the business community would like her to be more interested in how business functions, but she is not alone in that. The council talks jobs, but the members don't know how jobs happen."

Mason, who expects to continue to head the council's education committee, also has a close relationship with the mayor. Mason and her husband were among the group of Washington residents who attended a party in the late 1960s to welcome Barry as head of the Student Non-Violent Coordinating Committee's Washington office.

"Charlie knew him before I did," Mason said, making one of her frequent references to her husband, who has rarely left her side since their marriage in 1965 and serves as her chief adviser.

When Barry, as a council member, was wounded in the Hanafi takeover of the District Building in 1977, he spent the first few days out of the hospital recuperating at the Masons' home in Northwest Washington. Barry's political organization gave Mason crucial support in her successful council race the following year.