William E. Simons, the only president the Washington Teachers Union has ever had, is facing an unexpected election challenge from former supporters after a federal court judge threw out the last union vote because it was improperly conducted.

Simons easily defeated three-time opponent James D. Ricks in the regular union elections last May and seemed assured of another two-year term. But Ricks' charges that the results should be invalidated eventually persuaded the U.S. Labor Department to seek to overturn the election in court.

U.S. District Court Chief Judge Aubrey E. Robinson Jr. ruled in November that the election was not conducted by secret ballot as required by federal law, and ordered a new election that will be monitored by the Labor Department. In the meantime, two union leaders who supported Simons as recently as the May election are seeking to oust him.

It is perhaps the most serious challenge to Simons' stewardship of the union since he became the union's first president in 1964.

"I consider it an honor to have served with William Simons, but teachers in the schools have drafted me to run and they have decided they want a change," Jimmie D. Jackson, director of the D.C. Teacher Center, said yesterday at a news conference at Howard University. "I want to alleviate some of the apathy at the rank-and-file level and bring more effective representation of teachers' concerns."

Jackson has served as the union's general vice president, its second highest office, since 1979, and twice ran on a slate with Simons.

Also challenging for the presidency is former Simons supporter William I. Stewart, the union's vice president for vocational schools.

"I wouldn't even be running if things were not in desperate straits. Morale in the membership is about rock bottom," Stewart said.

Some observers say they believe the decision of Jackson and Stewart to challenge Simons exposes a rift in the union that could favor Ricks, who will take on Simons for a fourth time. "This is the first opportunity to run in an honest, fair election," said Ricks, who has taught in D.C. schools since 1967. "I won the court case and I won the right for everybody to vote."

Simons counters that the court found no instances of ballot tampering or intimidation, only that the May election was not conducted in total secrecy. Simons says he was surprised by Jackson's challenge but still predicts a victory.

"This is the most I have faced at one time, but it is still looking very good as far as I'm concerned," Simons said yesterday, scoffing at the suggestion that his base of support might be eroding. "Any individual member of the union could find a group of teachers who would indicate that they should run. That does not mean that there is broad-scale support for that individual."

Ballots for the election will be mailed to the 4,200 union members March 1 and must be returned by March 18 to a post office box controlled by the Labor Department. Ballots will be counted March 19 under Labor Department supervision.