School officials have apologized for allowing a high school "Slave Day" that was offensive to some blacks in Ridgecrest, about 70 miles northeast of Bakersfield. "I have nothing against fund-raisers. But I do not understand why anyone would want to make a mockery of such a brutal institution," W. E. Collier, local president of the National Assn. for the Advancement of Colored People, told the Sierra Sands Unified School District Board of Education. He said Supt. Anthony Magliari had apologized on behalf of the district. The event, also called "Rent-a-Senior Day," was held last month at Sherman E. Burroughs High School to raise money for homecoming activities by auctioning off the services of seniors.