The Supreme Court said Monday it will decide the extent to which public schools can use race in deciding school assignments, setting the stage for a landmark affirmative action ruling.

Justices will hear appeals from a Seattle parents group and a Kentucky parent, ruling for the first time on diversity plans used by a host of school districts around the country.

Race cases have been difficult for the justices. The court's announcement that it will take up the cases this fall provides the first sign of an aggressiveness by the court under new Chief Justice John Roberts.

The court rejected a similar case in December when moderate Justice Sandra Day O'Connor was still on the bench. The outcome of this case will turn on her successor, Samuel Alito.

In one of the cases, an appeals court had upheld Seattle's system, which lets students pick among high schools and then relies on tiebreakers, including race, to decide who gets into schools that have more applicants than openings.

The lower court decision was based in part on a Supreme Court ruling three years ago, written by O'Connor, which said that colleges and universities could select students based at least in part on race.

The court also will also consider a school desegregation policy in Kentucky. That case is somewhat different, because the school district had long been under a federal court decree to end segregation in its schools. After the decree ended, the district in 2001 began using a plan that includes race guidelines.

A federal judge had said system did not require quotas, and that other factors were considered including geographic boundaries and special programs.