THE APPOINTMENT of a superintendent is a local board of education's most important task, and the timing of the actual search is often crucial. If the search begins too early in the school year -- in the fall -- the selecting school board may attract few superior applicants because most sitting superintendents and administrators are deeply involved in their current jobs. If the search begins too late -- at the end of the school year -- the board may find that it has missed opportunities and that the best candidates have already filled vacancies elsewhere.

The D.C. Board of Education has already announced its intention to find a replacement for School Superintendent Andrew E. Jenkins, whose contract expires next June. Fortunately, in terms of timing, the D.C. school board finds itself in the best possible position, but the time to start the preliminaries is now, and several basic decisions should be made in the next few weeks.

Will the board seek advice from business and community leaders, as many other large school districts have done in recent years? That decision should be made now, because, if the answer is yes, it will take time to develop the necessary advisory panels. Will the board again conduct its selection on its own, or will it choose to seek as well the services of experts and private firms that match prospective candidates with a school system's particular needs? Again, now is the time to decide. And what exactly is the board looking for in a new superintendent?

This time the board should be sure of these things before it starts to move. Back in 1988, for example, the board wasn't sure whether it wanted an experienced insider or an outsider with proven leadership credentials. It wound up looking for both, and the initial applicant list was small and rather unimpressive. Why? People who have studied superintendent searches say that high-quality administrators from other jurisdictions aren't likely to get involved and take the risks of seeking a new post if the selecting school board hasn't decided whether it really wants an outsider. They also say the D.C. school board should be prepared to accept applications by early 1991. The board can then comfortably make its choice in the spring, giving the new superintendent time to take the reins next fall.

If the school board does its job properly and promptly this time around, it stands a much better chance of selecting the kind of leader the school system so desperately needs.