The court accepted cases from Seattle and Louisville, Ky., for its next term. The school districts in both cities defeated challenges to their assignment procedures in the lower courts.

"Looming in the background of this is the constitutionality of affirmative action," Davison Douglas, a law professor at William and Mary, said in an interview with The Associated Press. "This is huge."

In addition to the inherent interest in the cases, there is the added suspense created by the presence of two new members of the high court, Chief Justice John G. Roberts Jr. and Justice Samuel A. Alito Jr., whose conclusions on race-related matters will be eagerly awaited.

The court ruled three years ago that colleges and universities can take race into consideration when selecting their student bodies. Now it will decide whether the same logic ought to apply to public high schools. The ruling on colleges and universities was written by Justice Sandra Day O'Connor, who has since retired.

Seattle school administrators have wrestled for decades with the de facto segregation that tends to mirror the housing patterns of white, black and Asian families in the community. Students can pick among high schools. But since some schools have more applicants than they can handle, the district relies on tie-breakers, including race, to decide who gets into the over-subscribed schools. A group called Parents Involved in Community Schools sued in 2000, contending that it was unfair for the school district to consider race.

The plan was upheld by the Washington State Supreme Court, which found that it did not violate the state's Civil Rights Act, as its opponents argued. But it was struck down by a three-judge panel of the United States Court of Appeals for the Ninth Circuit — and then upheld by a 7-to-4 vote of that court, which overruled the smaller panel.

The seven judges in the majority concluded that the Seattle plan was narrowly enough tailored that it did not violate the Equal Protection Clause of the 14th Amendment to the Constitution.

That finding was welcomed by the NAACP Legal Defense and Educational Fund, whose director-counsel and president called it a step "to ensure truly equal access to educational opportunities for all students and to overcome long-maintained patterns of exclusion that have stigmatized and harmed African-American and other minority citizens of our country."

The Kentucky case arises from a suit filed by Crystal Meredith, who contends that her son Joshua was not allowed into the neighborhood school because he is white. The Jefferson County school district has a history different from Seattle's, in that the Louisville schools operated for years under a federal order to desegregate. In 2001, the district began using a plan that includes racial guidelines.

The cases are Parents Involved in Community Schools v. Seattle School District, No. 05-908, and Meredith v. Jefferson County Board of Education, No. 05-915.