Some call it a necessary step to heal long-standing racial inequality. Others call it a system of racial discrimination no better than apartheid in South Africa. It's affirmative action on campus -- and thanks to the Supreme Court, the controversial practice of reserving slots for students of certain racial and ethnic backgrounds is back in the public eye.

On Dec. 2, the Supreme Court agreed to hear two cases involving challenges to the admissions practices of the University of Michigan -- one involving the undergraduate program and one involving the law school. The cases reopen a long-unsettled wound and provide the Court a welcome opportunity to clarify the law in this difficult area.

Since 1978, when the Court decided a case involving the application of a white male, Alan Bakke, to the University of California, the status of racial preferences on campus has been in flux. In Bakke v. California, four justices (including two still on the Court today, Stevens and Rehnquist) wrote that weighing race in school admissions is never permissible. Four other justices disagreed, insisting that race is fair game. Indeed, they said, a school might wish to make up for past discrimination by creating a strict quota system, reserving a set number of spots for minority applicants.

Justice Lewis Powell took the middle ground. He concluded that strict quotas are unconstitutional, but that an admissions policy that took race into account as a "plus factor" was permissible, just as a policy that accounted for an applicant's athletic prowess or status as the child of an alumni was permissible.

The problem is twofold. For one, race is different. And the use of race as a "plus factor" can and has become a de facto quota system (and therefore an enormous "negative factor" for the qualified students who lose out).

There is no real factual dispute in the Michigan cases. Qualified white students seeking admission to the university are significantly less successful than similarly qualified minorities in gaining admission to the university. At the law school, for example, a white applicant with average test scores and grade average is admitted 22 percent of the time; for a minority applicant with identical scores, the admission rate is 100 percent.

School officials don't deny the disparity. Rather, they justify it as necessary to ensure a diverse school population. By considering race, they say, they're compensating for other societal disadvantages that minority student encounter when trying to learn. Besides, they add, all students learn better in a diverse school, and graduates of a diverse school are better prepared to participate in a pluralistic, democratic society.

Thus, the question squarely before the Supreme Court is whether such policy justifications are enough. In the language of the law, the question is whether Michigan's admissions policy is "narrowly tailored" (that is, uses the least intrusive method) to serve a "compelling governmental interest."

There is substantial doubt on both points. In states such as Georgia, Texas and California, where racial preferences in school admissions have already been outlawed, the state universities have continued to attract minority students by other means. They have, for example, increased efforts to recruit minority students through outreach and marketing. In the process, they've shown that explicit racial preferences may not be necessary to achieve a diverse student body.

But is the goal of creating a diverse student body a sufficiently compelling reason to instill racial quotas on campus? If "to get beyond racism we must first take account of race," as Justice Harry Blackmun said in Bakke, the cure may be worse than the disease.

As Justice Scalia has written, "The difficulty of overcoming the effects of past discrimination is as nothing compared with the difficulty of eradicating from our society the source of those effects, which is the tendency -- fatal to a nation such as ours -- to classify and judge men and women on the basis of their country of origin or the color of their skin." The renowned legal scholar Alexander Bickel put it even more plainly: "Discrimination on the basis of race is illegal, immoral, unconstitutional, inherently wrong, and destructive of democratic society."

More than 100 years ago, the Court in one of its most tragic decisions approved the concept of "separate but equal" public accommodations for different races. In dissent, Justice John Harlan made a point that's just as true today: "Our Constitution is color-blind, and neither knows nor tolerates classes among citizens." Will Michigan officials ignore that lesson?

Paul Rosenzweig is senior legal research fellow in the Center for Legal and Judicial Studies at the Heritage Foundation and adjunct professor of law at George Mason University.