Georgetown University law professor Eleanor Holmes Norton won a decisive victory in the Democratic primary for D.C. delegate last night despite the last-minute disclosure that she and her husband had failed to file D.C. tax returns for the past seven years.

Norton held off an 11th-hour surge by D.C. Council member Betty Ann Kane (At Large), who was buoyed by an extremely strong showing in Ward 3, west of Rock Creek Park. Kane also won Ward 2, which includes Georgetown, Foggy Bottom, and parts of downtown and Southwest Washington.

But Norton carried the other six wards and won 40 percent of the vote compared to 33 percent for Kane. Norton's vote, 46,620, was 4,426 more than Sharon Pratt Dixon's total for the Democratic mayoral nomination.

Trailing far behind Norton and Kane were former D.C. Council chairman Sterling Tucker, with 11 percent; former city official Joseph P. Yeldell, 7 percent, and former congressional aide Donald M. Temple, 6 percent.

In the Republican primary, former Reagan administration official Harry M. Singleton won with 69 percent of the vote, final returns showed. Political consultant Jim Champagne had 23 percent and contractor Roffle Mayes Miller Jr. had 8 percent.

Appearing before about 200 cheering supporters at the Washington Plaza Hotel, Norton claimed victory and thanked D.C. voters, "who never lost their faith and confidence in me," she said.

Kane left her campaign headquarters last night without conceding, saying she wanted to wait for the absentee ballots to be counted Sept. 23. However, unofficial final returns showed Norton with a 5,194-vote lead over Kane and only 4,800 absentee ballots.

Norton, a former chief of the U.S. Equal Employment Opportunity Commission making her first bid for public office, sought to portray herself as a fresh face in D.C. politics who would parlay her considerable national reputation into increased respect for the District on Capitol Hill.

But she came under sharp criticism from Kane and her other rivals as an interloper who was scarcely interested in District affairs until she mounted her congressional candidacy in May. Kane repeatedly criticized Norton for her failure to vote in four of the past 10 D.C. elections.

But Norton ignored the criticism and outstripped her rivals in fund-raising. She secured several valuable endorsements, including one from the metropolitan area AFL-CIO, and she surged to a lead in the polls that, despite her late difficulties, was borne out.

Late Friday, someone anonymously faxed to news organizations a document indicating that Norton and her husband were delinquent on $10,755 in D.C. income taxes from 1982. With penalties and interest, the document stated, Norton and her husband, Edward Norton, owed $25,381.80 as of Jan. 18, 1989.

Norton acknowledged the next day that her family had failed to file D.C. income tax returns -- a misdemeanor under D.C. law -- for the last seven years. She tried to defuse the situation by asserting that her husband, a former chairman of the D.C. Board of Elections and Ethics, handles the family's finances and that she had not known of the failure to file. But her rivals, handed an unexpected opportunity after a summer of trying to catch up, sharpened their attacks.

Tucker, who had been No. 2 in a Washington Post poll, called on Norton to drop out. Kane lined up an endorsement from Ward 3 D.C. Council member Jim Nathanson.

Interviews with voters yesterday showed that Norton was hurt some by the weekend's revelations, especially in Ward 3.

Mark Ehlers, 31, an assistant U.S. attorney voting at Murch Elementary School at 36th and Ellicott streets NW, said he had been considering Norton, but added, "I must admit the business with the taxes made me lean to Kane."

But there was also sympathy for Norton, who said Monday that "no dirty tricks" were going to drive her from the race.

David V. Crow, 71, a retired Air Force man who said he voted for Norton, applauded the way Norton handled the disclosure of her tax problems. "She had her husband by the ear and said, 'Come on out here with me,' " he said.

The delegate's race was one of several contests thrown into confusion this year by Mayor Marion Barry's arrest on drug charges in January. Barry was subsequently convicted of misdemeanor drug possession.

While Barry was undergoing substance abuse treatment after his arrest and before his trial, incumbent Del. Walter E. Fauntroy made the surprise decision to give up the post he had held for 19 years to run for mayor.

That triggered a full-scale political brawl.

In addition to Kane, a three-term council member who had long coveted Fauntroy's position, veteran politicians Tucker, Yeldell and former school board member Barbara Lett Simmons signed up to run. Simmons later dropped out of the race.

Norton will face the Republican nominee, Singleton and George X Cure, a member of the Nation of Islam running as an independent.

Singleton is an attorney and former chief of civil rights enforcement in the U.S. Education Department who has argued that the job of non-voting delegate needs to be "redefined."

He said during his campaign that Fauntroy spent too much time focusing on national politics and ignored the city's deteriorating financial condition and other problems. While he said statehood for D.C. was not a priority, he promised to seek a vote for the delegate on the House floor.