THE MUCH-MALIGNED D.C. School Board showed rare wisdom in delaying its decision on Superintendent Floretta McKenzie's recommendation to close 14 city schools. When it meets again tomorrow to vote on the closings, the board has a chance to earn the city's thanks for years to come.

Closing schools to save money may be a classic case of shortsighted public policy. While declining enrollments in public schools make many buildings seem expendable now, by the end of this decade more children will be entering public schools and new buildings will be needed at much greater cost.

The School Board's vote on April 10 did more than just put off a decision on which schools to close and sell. The board directed the superintendent to look for ways to use the surplus schools by leasing or sharing them with businesses, community groups and government agencies. That move, if sustained in Monday's board meeting, opens up a whole range of intriguing possibilities.

Several such ideas have been considered here since 1980, when Sen. Patrick Leahy of Vermont, then chairman of the Senate District Committee, agreed after an earlier school-closings controversy that "the best solution would be retention of the facilities . . . for other educational purposes or use by other District government agencies."

One idea considered was to turn schools with excess space into mixed-use, joint-occupancy school/community centers operating year-round from early morning to late at night. Under such a plan, any space temporarily or permanently unneeded for school purposes could be made available to community agencies, nonprofit groups or even businesses rent-free or at nominal rent.

A possible model for Washington is Baltimore's Paul Lawrence Dunbar Community High School, with a range of activities operating before, during and after school hours that includes:

Cultural arts: classes in crafts, dance, music, film-making, photography and theater.

Community recreation: indoor and outdoor programs including camping.

City hall office: a local branch of the mayor's office.

Social services office: provides counseling and information on public assistance programs, food stamps, medical aid.

Day care center for preschoolers.

Harbor City Learning Center: an alternative high school.

Neighborhood Social Security office administering retirement benefits and health insurance programs.

Manpower office: skills training, job development and placement services.

Legal aid office: advice and representation for low-income families.

Youth services center: counseling and guidance for ages 7 to 18.

Several variations of the same theme have succeeded in Washington. In Georgetown's Jackson School, the A-Salon art gallery and school has turned an eyesore into a community resource. On Capitol Hill, the Edmonds Building houses the D.C. teachers' credit union and Associates for Renewal in Education, a nonprofit educational consulting firm that has made valuable contributions to the D.C. public schools. At Lincoln Junior High School, the Bilingual/Multicultural High School is operating successfully, funded by the Labor Department through Project SER, a national Chicano career training organization.

One of the best local examples of the shared-space concept at work is School Board president David Eaton's own All Souls Church, a beehive of community activity from dawn to midnight. There are no security problems, and the learning experiences are multiplied by the diversity of the organizations and people using the building.

Under the present rules, any organization using public school space in the District must pay rent to the D.C. treasury or supply the school system with some kind of services in lieu of rent. Mayor Barry and the City Council should change the law to allow rent to be paid directly to the School Board. This would provide the schools with much-needed operating revenues from a source outside the tax base.

The short-term benefits, however attractive, pale in comparison with the long-term savings to the already overstrained city and federal treasuries. "In the 1980s," the National Institute of Education reported four years ago, "elementary enrollments are expected to increase" as the children of the baby boom years "begin to settle down and have children of their own." The federal institute's report emphasizes that "there are very likely to be as many children in elementary school in 1995 as there were in the peak year of 1970."

In Washington, two factors make this national projection even more critical: First, the birth and immigration rates for blacks, Hispanics and other minorities are considerably higher than tose for whites. Second, the limited boundaries of the District eliminate the possibility of significant land acquisition by the city in the future.

By holding on to existing properties, which can be refurbished a decade hence at considerably lower cost than what it would take to buy land and build new schools, the School Board can thus serve the needs of both the present and the future.