The Washington Teachers Union won the right to continue as bargaining agent for the District's 5,700 public school teachers last night, defeating the National Education Association-D.C. in a representation election by a margin of more than three to one.

The election turnout was one of the largest ever for city teachers, as about 80 percent cast ballots between 9 a.m. and 3 p.m. at 45 schools throughout the city.

WTU officials described the victory as a "clear indication" that teachers are united and supportive of the union that has served as their bargaining agent since 1967.

Recently elected WTU president Harold Fisher said that the vote was "a mandate for me to keep headed in the direction that I have started."

Fisher was elected to the presidency last month, ousting William Simons, who had held the post for 20 years.

A spokeswoman for the American Arbitration Association, which supervised yesterday's election, said that a final but unofficial count showed that 3,647 votes were cast for the WTU and 1,127 for the NEA.

She said that 68 ballots were challenged and 65 others were not counted because of procedural questions.

The results will be certified "as soon as possible," she said.

The WTU, an affiliate of the American Federation of Teachers, was forced to submit to the election after about 2,000 teachers signed a petition last February declaring that they wanted to be represented by the NEA, according to officials of the D.C. Public Employee Relations Board.

NEA officials charged during the campaign that the WTU had become weak and ineffective, and NEA organizers promised city teachers more aggressive leadership, better salaries and benefits and professional resources to help them improve their skills.

Despite yesterday's results, NEA supporters said last night that their campaign had not been totally unsuccessful.

Julie Henderson, who teaches Spanish at Shaw Junior High School, said: "This election has gotten the WTU off its butt. It's gotten them to move. They realize that we are not satisfied with the gains made in the past."

WTU's backers, however, celebrated the victory as proof that the union has the overwhelming support of D.C. teachers.

The "stunning victory is quite sweet," Fisher said, adding: "It is a moving and invigorating experience to witness such a display of teacher unity."

The votes were counted between 6 p.m. and 8:30 p.m. at Friendship Community School in Southeast.

After the results were announced, a number of the teachers present cheered and began chanting: "Go home, NEA."

Barbara Lipscomb, an English teacher at Francis Junior High School and an at-large member of the WTU's executive board, said that the city's teachers had been sharply divided during last month's Fisher-Simons election, but the NEA challenge made them rally together to "save our union."

"This campaign has mended some wounds," she said.