The race for the school board seat in Ward 3 has turned into one of the city's most expensive board contest ever, pitting two well-known community activists who claim strong backing from distinct, but equally active, groups of supporters that are both likely to show up at the polls Nov. 3.

Mary Ann Keeffe, a 37-year-old economist, has raised $12,000, far more than any other school board candidate this year. Keeffe, a longtime worker in the heavily Democratic politics of Ward 3 for the past 10 years, has helped out in dozens of other campaigns and is making her first run for public office.

Keeffe faces a spirited but less well-financed campaign by Wanda Washburn, 59, who has served as president of three different home and school associations in the ward and has an 11-year record of involvement in the city's public schools. Washburn has raised about $5,800.

Washburn and Keeffe are vying to succeed 7-year incumbent Carol Schwartz, who announced earlier this year that she would not run for reelection. Schwartz said her two board campaigns cost a total of $8,000.

Keeffe and Washburn have appeared at numerous civic and meet-the-candidate functions and acknowledge that they have no major disagreements on issues, with each depending on a core of support to get out the vote.

Both have deplored the in-fighting and factionalism that have marred school board politics, pledged support for new School Superintendent Floretta D. McKenzie, been critical of school board meddling in day-to-day operations of the schools, and called for better financial and professional accountability for sharply reduced budgets and declining enrollments.

"If you go to the candidate forums, we all agree on the same things. We have different approaches," Washburn said.

Concerns commonly expressed about the schools in Ward 3 include the quality of teaching, disruptions caused by budget cutbacks, and discipline problems in junior and senior high schools.

But they have differed on who has the best qualifications for the 4-year term with an annual salary of $18,000.

"My political experience is needed" on the strife-torn school board, Keeffe said. "The school board needs to be integrated with the politics of the city."

Washburn counters that her record in the schoolrooms and parent organizations during the past decade and her involvement in the school budget fights make her qualified to serve on the board.

Although the school board election is officially nonpartisan, Keeffe is campaigning with financial and political support from well-known Democrats, including Council Member Polly Shackleton, who serves on her campaign committee and has campaigned hand-in-hand with Keeffe.

Keeffe also has garnered $50 contributions from council members John Ray, a candidate for mayor, and David A. Clarke. Sterling Tucker, former council chairman who is making a second try for mayor, also has chipped in $50. Council Member Betty Ann Kane (D-At Large), a former school board member, also is supporting Keeffe.

Democratic Party stalwarts W. Averell and Pamela Harriman hosted a $20-a-person fund-raiser for Keeffe last month in their Georgetown home, the first exclusively local fund-raiser the celebrity couple has sponsored.

Washburn has scored heavily with school groups in the ward, gaining the endorsement of virtually all of the elected leaders of the ward's parent and school groups. She also has been endorsed by the Washington Teachers Union and the D.C. Citizens for a Better School Board, a new 30-member group that includes former school superintendent Vincent Reed and Schwartz.

Supporters of Washburn say Keeffe has improperly tried to make the nonpartisan election a partisan affair. Washburn is a registered Republican in a city that has a 3-to-1 Democratic registration. Keeffe's critics also have said she is using the school board race as a base for future political campaigns.

While Keeffe acknowledges her effort has a distinct Democratic flavor, she says she is trying to broaden her base and says she is looking no further politically than a 4-year term on the board.

Washburn's critics say her school experience as president of her daughter's successive elementary, junior and senior high parent-school groups was not much more than the "baking cookies" level of school involvement and they say she does not have the political skills needed for the school board job.

Washburn acknowledges that "I have baked a lot of cookies," but recites a list of other school-related activities, including testifying before the City Council and U.S. Congress on school budget problems and serving on a variety of school improvement committees, including Parents United for Full Funding which she helped form.

Washburn, whose supporters have blitzed the ward with campaign posters, and Keeffe, whose brochures are artfully produced, have developed well-run, professional operations in a race that in 1977 brought out fewer than 10,000 voters to the polls.

This year's expected turnout is clouded by an "X" factor -- the controversial education tax credit initiative that the D.C. Court of Appeals has ruled will be on the ballot.

The initiative would allow up to $1,200 per pupil in income tax credits for individuals or corporations who pay tuition or other education expenses at either private or public schools.

Both Keeffe and Washburn have criticized the initiative, saying it would strain the public schools' already weakened financial condition. But neither candidate is certain what effect the initiative will have on their campaigns or voter turnout.

Ward 3, which contains the most affluent residential sections of the city, lies west of Rock Creek Park from Georgetown to Chevy Chase. Its 15 public schools include elementary schools with some of the city's lowest enrollment, some with less than 200 students attending, but also have some of the highest achievement scores in the city.

The ward also has the greatest concentration of private and parochial school students whose parents would be the most enticed by school tuition tax credits.

Washburn, who has a daughter who is a senior at Wilson High School, said her first involvement in city schools was in 1970 as a math and reading tutor at Murch Elementary. She also has been a member of the Board of Advisors for the D.C. Elementary and Secondary Education Act Program and the Education Coalition of D.C. Citizens for Better Public Schools.

Keeffe, an economist employed part time by the Library of Congress Congressional Research Service, has four children, two at Janney Elementary and two not yet of school age. She is a former chairman of the Ward 3 Democratic Committee and is a current member of the D.C. Democratic State Committee.