The U.S. Labor Department announced yesterday that it will not certify the Washington Teachers Union election that longtime union president William H. Simons lost by four votes last month, and said it will ask a federal judge to order a new election.

A department spokesman said the decision, which must be approved by U.S. District Court Judge Aubrey Robinson Jr., was based on the discovery of "inadvertent mistakes" in voter lists and on interviews with union members who said they did not vote even though their mail ballots were counted.

Both complaints were raised by James D. Ricks, the apparent winner in the vote, which was counted March 19.

In that election a running mate of Ricks, Jeanette Feeley, was elected general vice president, the union's second highest post, but the other 20 union offices on the ballot were won by Simons' supporters.

The March election, conducted by mail ballot and monitored by Labor Department officials, was ordered by Robinson after he overturned a 1981 vote in which Simons defeated Ricks.

Robinson ruled that the 1981 voting was not conducted by secret ballot.

Yesterday, Simons, who has led the teachers union since its inception in 1964, said he welcomed the Labor Department's decision, and added, "I am confident that the results will be different the next time around."

Ricks, chairman of the science department at Ballou High School, expressed disappointment.

"They want to throw the entire election out based on a bad mailing list and the fact that someone voted for other people," Ricks said.

"I should not have to be punished for that."

After the March election Simons asked for a recount, and lawyers for the two candidates argued over 17 challenged ballots that were not tallied. Yesterday a source said the challenged ballots were not a significant consideration in the Labor Department decision because the lack of a correct mailing list of voters and doubts that all ballots were properly cast had called the entire election into question.

Ricks outpolled Simons 1,146 to 1,142 in the vote, which was by far the largest in the union's history.

The union, an affiliate of the American Federation of Teachers, AFL-CIO, has about 4,200 members. It bargains on behalf of about 5,500 teachers, librarians, psychologists, and other nonadministrative professional employes of the D.C. public schools.

Yesterday supporters of Ricks dominated the union's regular monthly meeting at Roosevelt High School on 13th Street NW.

After two close votes to speed up procedures for selecting new members of the union's elections committee, which Simons had opposed, many supporters of the union president left the meeting.

A quorum call fell 36 short of the 100 members needed to conduct business, and Simons adjourned the meeting. As Simons left the auditorium, Ricks' supporters sang "We Shall Overcome."

Feeley later told them it was unfortunate that complaints brought by Ricks were being used to invalidate his election, but she said, "We had to do it. We're people of integrity."