The District of Columbia City Council reversed itself last night and voted to hold a citywide election May 1 to fill a vacancy on the school board.

By a vote of 9 to 3, the council declared an emergency, then unanimously passed the measure. It directs the city's Board of Elections and Ethics to list school board candidates on the ballot of a special election for two City Council seats already scheduled for that day.

The citywide vote had been sought by the school board, which, under city law, normally must appoint somebody to fill a vacancy. The faction-ridden board wanted to avoid that controversial chore.

The at-large vacancy on the board was created by the election in November of Betty Ann Kane to the City Council. The May 1 election was called to fill an at-large council vacancy created by election of Marion Barry as mayor and a Ward 4 vacancy created by election of Arrington L. Dixon as council chairman.

Two weeks ago, the council failed to muster the two-thirds majority of its membership needed to declare an emergency. Jerry A. Moore Jr. (R-At Large) argued successfully last night to overturn that decision.

The council action is subject to approval of the mayor.

Dixon argued against the election proposal, sponsored by Hilda H. Mason (Statehood-At Large). Dixon contended that holding an election on 83 days notice would be unfair to anybody but "insider" candidates.

Only Willie J. Hardy (D-Ward 7) and William R. Spaulding (D-Ward 5) joined him in voting against declaring the emergency, an action that procedurally short-cuts the measure's enactment time and averts the need for congressional review.

Mary S. Rodgers, elections administrator for the Board of Elections, said nomination petitions for council candidates at the May 1 election are to be filed by next Tuesday.

Rodgers said the board can adopt special rules to reduce the normal 44day period for circulating petitions, as well as the requirement for collecting 1,000 valid signatures to qualify for the ballot.