WASHINGTON voters will have an opportunity to shape the composition of the D.C. Board of Education in November at a time when the board will be deeply engaged in its most important task -- selection of a new school superintendent. Three years ago, those who had been elected to represent Wards 2, 4, 7, 8 and one at-large seat took part in the selection of the incumbent, who ultimately failed to rise to the demands of the job. It is fitting under these circumstances that the same school board posts are to be filled again.

The evidence of recent school board elections is that many more people are watching, judging and voting for those posts. In 1983, for example, at-large board member Eugene Kinlow needed just 19,273 votes to win his citywide seat on the board. By 1987, Mr. Kinlow needed 31,606 votes to win a similar percentage of the overall vote.

With one month to go before the Aug. 29 filing deadline, the huge number of prospective candidates shows that interest is keen. Some 26 challengers have already requested voter petitions to get on the ballot. Those running for ward-level seats need 200 signatures from registered voters, and those vying for the at-large post need 1,000.

The bulk of the challengers -- 22 so far -- are seeking signatures for the Ward 4 and the at-large seats. Mr. Kinlow is not seeking reelection this year, and Ward 4 incumbent Linda Cropp hopes to move to the D.C. Council. The list includes a mix of past and present PTA presidents, teachers and others who have been deeply involved in the schools.

At this point, there appears to be significantly less interest in running against incumbents R. David Hall in Ward 2, who is unopposed so far, and Nate Bush in Ward 7, who may face only one opponent. Three people are seeking enough signatures to take on Ward 8's R. Calvin Lockridge. These are important electoral seats, and the incumbents have hardly performed so well that they deserve to cruise into a new term without a serious challenge.

The difficulties facing the school system are formidable, and the new school board will have to pick a superintendent with the vision and strength to handle them. That is what the voting public must consider now.