The City Planning Commission on Wednesday approved the construction of a $25 million biomedical laboratory on the site where Malcolm X was slain, provided a substantial portion of the building is preserved. That includes 40 percent of the Audubon Ballroom, including the stage on which the black nationalist leader was shot o Feb. 21, 1965. In May, the commission had deferred a decision on a plan to demolish the ballroom at Broadway and 165th Street, across from Columbia-Presbyterian Medical Center. Followers of Malcolm X objected. Applicants for the research building were Columbia University and the city. It is to get funding from the Municipal Assistance Corp. and state urban development aid. The project still has to be approved by the city's Board of Estimate. Malcolm X headed the Harlem mosque of the Black Muslims but split with Black Muslim leader Elijah Muhammad in 1963. Malcolm X then formed the Organization of Afro-American Unity, which promoted black nationalism but admitted the possibility of interracial brotherhood.