After four gritty years working on the road for the Santa Clara County transportation agency -- patching holes, shoveling asphalt, opening culverts -- Diane Joyce applied in 1980 for a less strenuous desk job as a road dispatcher. At the time not one of the California agency's 238 skilled positions was held by a woman. Joyce knew, however, that two years earlier the county had enacted a voluntary affirmative-action policy designed to correct that imbalance.
Paul Johnson, a white male who had worked for the agency for 13 years, also applied. He and Joyce were among the seven applicants who scored...