WASHINGTON - The decades-long wait for the Supreme Court to return to the heated topic of affirmative action in university admissions ended yesterday when the justices announced they would review two cases challenging the University of Michigan's consideration of race to ensure a diverse student body for its law school and undergraduate program.

Coming a generation after the Bakke decision in 1978 invalidated the use of fixed racial quotas but upheld diversity as a valid goal, the new cases, to be decided by early summer, are certain to attract enormous attention and to renew a debate that has never completely died down.

The court in these cases could prohibit the use of race in university admissions, allow its widespread use to continue or pronounce new standards for evaluating affirmative action case by case.

Getting the issue back on the Supreme Court's docket is the culmination of a long litigation campaign by a public interest group here, the Center for Individual Rights, which opposes affirmative action and helped recruit the three unsuccessful white applicants who are the plaintiffs in the two cases.

One, Barbara Grutter, applied to the University of Michigan Law School, one of the most selective in the country, in 1996 at the age of 43. The two white students who failed to win admission to the university's College of Literature, Science and the Arts, the basic undergraduate program, are Jennifer Gratz and Patrick Hamacher. Both were B students at Michigan high schools who argued that the admission of black and Hispanic applicants with similar or lesser academic records was a violation of the constitutional guarantee of equal protection. The program received more than 25,000 applications for 5,187 places this year.

The 6th U.S. Circuit Court of Appeals in Cincinnati upheld the law school's admissions program in a bitterly divided 5-4 decision this year. The U.S. District Court in Detroit upheld the undergraduate admissions program two years ago in a decision that found an earlier, more rigid version unconstitutional. The appeals court heard the undergraduate case a year ago but has not yet ruled on it, and yesterday the Supreme Court granted the plaintiffs' request to accept a direct appeal from the district court without waiting any longer.

The cases present the same two legal questions. The first is whether diversity is a "compelling state interest," the test the court applies to any governmental policy that takes race into account. The second is whether, if that test is met as a general matter, the specific program under review is "narrowly tailored" to accomplish the goal with as little harm as possible to competing interests.

The first question is an almost abstract matter of constitutional doctrine, while the answer to the second depends on specific details. Michigan has vowed to defend its admissions programs vigorously, and the public can expect to learn a fair amount about admissions practices as they have evolved under a legal microscope at selective universities.

"We are looking forward to presenting our cases before the Supreme Court," the university's president, Mary Sue Coleman, said yesterday. "Our admissions policies have been carefully and thoughtfully designed and are based upon a great deal of research."

While the constitutional guarantee of equal protection applies directly only to government institutions, private universities also have a big stake in the outcome of the cases, Grutter vs. Bollinger and Gratz vs. Bollinger. That is because Title VI of the Civil Rights Act of 1964 bars race discrimination by any institution that receives federal money - essentially all universities except for some religious colleges. Michigan is likely to garner widespread support from the higher education community as well as from traditional civil rights organizations.

In its briefs, the university is arguing that with strictly race-blind admissions, it could not possibly build the "critical mass" of minority students necessary to make diversity more than an empty promise.

Despite its outreach and recruitment efforts, the university said, the law school received only 35 applications from minority students, compared with 900 from white students, at the top range of undergraduate grades and law board scores, which account for nearly all admissions. Even with a "race-blind lottery," the brief said, "the percentage of African-American students enrolled would almost certainly fall below 3 percent."

At the law school today, 74 of 1,109 students are black (6.7 percent) and 49 are Hispanic (4.4 percent). Students of Asian background are not considered "under-represented minorities" and do not benefit from affirmative action programs at Michigan. Among undergraduate students, 8.4 percent are black and 4.7 percent are Hispanic.