ASHINGTON, Nov. 2 - A California prison policy of temporarily segregating all new and newly transferred inmates by race came under attack at the Supreme Court on Tuesday in a case that pits the justices' tradition of deferring to prison administrators against their dislike of government policies that classify people by race.

California defended its policy, which the federal appeals court in San Francisco upheld, as necessary to prevent violence in a gang-ridden prison system.

"California is ground zero for race-based street gangs," Frances T. Grunder, a senior assistant state attorney general, told the justices. "The animosity between the gangs is purely race-based, and the racial pressures in prison are very, very severe."

More than 25 years ago, California adopted the practice of placing inmates in double cells with cellmates of the same ethnic background for the first 60 days after their arrival at a prison, either as newcomers to the system or following a transfer from another prison. The inmates are evaluated during that time for propensity to violence, among other things, and then are assigned permanent quarters on a nonracial basis.

Neither the federal Bureau of Prisons nor any other state follows such a policy, which the lawyer for a black inmate who challenged the system described as nothing more than "routine, blanket racial segregation." The lawyer, Bert H. Deixler, said it was based on a "needless and dangerous" stereotype that assumed that all members of a racial or ethnic group acted and thought alike.

California applied the policy last year to segregate 40,000 new prison inmates and several hundred thousand others who were transferred between prisons. On Tuesday, several justices questioned the rationale for applying the policy to transferred inmates.

"What's the justification?" Justice David H. Souter asked Ms. Grunder, observing that by the time of a transfer, prison officials had had "plenty of time" to assess an inmate's potential for violence. Justice Antonin Scalia was openly skeptical of the policy's application to transfers despite his apparent willingness to accept it for new inmates.

Justice John Paul Stevens wondered aloud whether placing inmates of the same race together might have the effect of increasing gang membership, by facilitating close contact between potential members of the same gang.

Garrison S. Johnson, the inmate who brought the lawsuit, is a black man who chose not to join a prison gang. "There is no record that he has ever been involved in interracial violence," his lawyer, Mr. Deixler, told the court. In prison since 1987, Mr. Johnson has been transferred five times, meaning he has encountered six periods of segregation. "He is in peril, unable to reach out across racial lines for support," Mr. Deixler said.

The Bush administration entered the case on Mr. Johnson's behalf to argue that segregation by race should always be regarded as presumptively unconstitutional and subject to the most exacting level of judicial scrutiny. The question in the case, Johnson v. California, No. 03-636, is what standard of judicial review should apply to the policy.

The United States Court of Appeals for the Ninth Circuit, in upholding it, applied the more deferential standard that the Supreme Court has developed for evaluating choices made by prison administrators. Both the inmate's lawyer and the administration are arguing that when it comes to race, the deferential stance should not apply.

Instead, they maintain, "strict scrutiny" should apply to prison policies that classify people by race, as to any such policies by government in any setting. Under strict scrutiny, a policy will be upheld only if it is narrowly tailored to achieve a "compelling" government interest.

"This case provides an opportunity to reaffirm that all government policies based on race are subject to strict scrutiny," Paul D. Clement, the acting solicitor general, told the justices. Mr. Clement said the federal Bureau of Prisons made housing assignments for prisoners based not on their race but on an individual evaluation drawn largely from the presentencing report that is prepared after conviction.

The strict-scrutiny position fits with the Bush administration's general view that race-conscious policies like affirmative action are constitutionally impermissible. Mr. Clement said the California policy would fail even a deferential standard of review if that standard were properly applied, but he tried to keep the justices focused on the strict-scrutiny argument. If the court agrees that strict scrutiny should apply, it will most likely return the case to the Ninth Circuit with instructions to re-evaluate the policy under that standard.

Chief Justice William H. Rehnquist, under treatment for thyroid cancer, was not at the court, but Justice Stevens announced that the chief justice would take part in deciding the two cases that were argued on Tuesday. Two years ago, when the chief justice missed two weeks of argument because of knee surgery, he voted in all the argued cases after studying the transcripts.