WASHINGTON (AP) – The Supreme Court on Thursday rejected integration plans in two major public school districts but left the door open for using race to assign students in limited circumstances.

The decision in cases affecting schools in Louisville, Ky., and Seattle could imperil similar plans in hundreds of districts nationwide, and it further restricts how public school systems may attain racial diversity.

The court split, 5-4, with Chief Justice John Roberts announcing the court’s judgment. The court’s four liberal justices dissented.

“The way to stop discrimination on the basis of race is to stop discriminating on the basis of race,” Justice Roberts said.

Yet Justice Anthony Kennedy would not go as far as the other four conservative justices, saying in a concurring opinion that race may be a component of school plans designed to achieve diversity.

To the extent that Roberts’ opinion could be interpreted to foreclose the use of race in any circumstance, Justice Kennedy said, “I disagree with that reasoning.”

“A district may consider it a compelling interest to achieve a diverse student population,” Justice Kennedy said. “Race may be one component of that diversity.”

He agreed with Roberts that the plans in Louisville and Seattle violated constitutional guarantees of equal protection.

Justice Stephen Breyer, in a dissent joined by the other liberals on the court, said Roberts’ opinion undermined the promise of integrated schools that the court laid out 53 years ago in its landmark decision in Brown v. Board of Education.

“To invalidate the plans under review is to threaten the promise of Brown,” Justice Breyer said.

While Justice Roberts said the court was being faithful to the Brown decision, Justice John Paul Stevens in a separate dissent called the chief justice’s reliance on Brown to rule against integration “a cruel irony.”

Justice Clarence Thomas, the court’s only black member, wrote a separate opinion endorsing the ruling and taking issue with the dissenters’ view of the Brown case.

“What was wrong in 1954 cannot be right today,” Justice Thomas said. “The plans before us base school assignment decisions on students’ race. Because ‘our Constitution is colorblind, and neither knows nor tolerates classes among citizens,’ such race-based decisionmaking is unconstitutional.”

The two school systems in Thursday’s decisions employ slightly different methods of taking students’ race into account when determining which school they will attend.

Federal appeals courts had upheld both plans after some parents sued. The Bush administration took the parents’ side, arguing that racial diversity is a noble goal but can be sought only through race-neutral means.

The Louisville case grew out of complaints from several parents whose children were not allowed to attend the schools of their choice. Crystal Meredith, a white, single mother, sued after the school system turned down a request to transfer her 5-year-old son Joshua Ryan McDonald, to a school closer to home.

Louisville’s schools spent 25 years under a court order to eliminate the effects of state-sponsored segregation. After a federal judge freed the Jefferson County, Ky., school board, which encompasses Louisville, from his supervision, the board decided to keep much of the court-ordered plan in place to prevent schools from re-segregating.

The lawyer for the Louisville system called the plan a success story that enjoys broad community support, including among parents of white and black students.

Attorney Teddy Gordon, who argued that the Louisville system’s plan was discriminatory, said, “Clearly, we need better race-neutral alternatives. Instead of spending zillions of dollars around the country to place a black child next to a white child, let’s reduce class size. All the schools are equal. We will no longer accept that an African-American majority within a school is unacceptable.”

Louisville Mayor Jerry Abramson said he was disappointed with the ruling because Louisville’s system had provided “a quality education for all students and broken down racial barriers” for 30 years.

He said he was confident school leaders effective new guidelines.

The Seattle school district said it used race as one among many factors, relied on it only in some instances and then only at the end of a lengthy process in allocating students among the city’s high schools. Seattle suspended its program after parents sued.

The opinion was the first on the divisive issue since 2003, when a 5-4 ruling upheld the limited consideration of race in college admissions to attain a diverse student body. Since then, Justice Sandra Day O’Connor, who approved of the limited use of race, retired. Her replacement, Justice Samuel Alito was in the majority that struck down the school system plans in Kentucky and Washington.

The cases are Parents Involved in Community Schools v. Seattle School District No. 1, 05-908, and Meredith v. Jefferson County Board of Education, 05-915.