The Supreme Court ruled yesterday that state workers who were discriminated against because of their age cannot sue under federal law, in a sharply divided opinion that continues the court's effort to curtail congressional power and could have repercussions for thousands of state employees nationwide.

By a 5 to 4 vote along familiar lines, the justices said Congress lacked the authority to make states liable for the age discrimination complaints of their workers. The ruling was a defeat for the nation's 5 million state employees and a variety of advocates for older and disadvantaged workers who had been part of the case. While those workers can still seek redress in state courts, the laws and enforcement vary widely around the country.

"The decision sends a message that if age discrimination is a civil right at all, it's a second-class right," declared AARP lawyer Laurie McCann.

But a spokesman for the Florida Board of Regents, which had been sued by a group of older professors, noted that the ruling still permits state workers who face discrimination to sue under the various state anti-bias laws. "The right place for this is with the states," Keith Goldschmidt said.

Writing for the majority, Justice Sandra Day O'Connor said that because an individual's age has not been granted the constitutional protection that race and sex have, Congress had insufficient grounds to override states' usual immunity from federal lawsuits. "Older persons . . . unlike those who suffer discrimination on the basis of race or gender, have not been subjected to a history of purposeful unequal treatment," O'Connor wrote.

Overall, the decision marked another stride in the court's quest to diminish the reach of Congress. It was announced, coincidentally, just minutes before the court heard arguments in another, more closely watched dispute over federal authority--concerning the 1994 Violence Against Women Act that allows women who have been sexually assaulted to sue their attackers in federal court.

Joining O'Connor in Kimel v. Florida Board of Regents were Chief Justice William H. Rehnquist and Justices Antonin Scalia, Anthony M. Kennedy and Clarence Thomas. Dissenting were Justices John Paul Stevens, David H. Souter, Ruth Bader Ginsburg and Steven G. Breyer. That is the same 5 to 4 split that emerged in a series of recent decisions limiting individuals' ability to sue for violations of federal law and on which yesterday's ruling was based.

Writing for the dissenters, Stevens attacked the majority's larger effort and asserted that, in the age discrimination dispute, Congress was validly overriding the normal protections given states in allowing workers to sue under the Age Discrimination in Employment Act, which protects workers 40 and older.

"It is . . . clear to me that if Congress has the power to create the federal rights that these [older workers] are asserting, it must also have the power to give the federal courts jurisdiction to remedy violations of those rights," Stevens wrote.

The case arose from a trio of lawsuits: three dozen professors and librarians at Florida state universities who claimed they were unfairly denied raises because they were over 40; a guard at a Florida prison who said he lost out on a promotion because of his age; and two professors, age 57 and 58, at an Alabama state school who said they were denied promotions and pay. The U.S. Court of Appeals for the 11th Circuit had ruled that the states could not be sued.

The Justice Department sided with the workers, arguing that the 14th Amendment gives Congress the power to enforce equal protection of the laws.

But the high court rejected those grounds, effectively saying that age cases are different from the traditional civil rights relating to race, national origin and sex. The court said that because state employers may differentiate among workers based on age in many situations, it is too extreme to hold them financially responsible in federal court for such decisions. The justices noted that states may favor younger workers if there is a legitimate reason to do so.

"Old age," O'Connor wrote, "does not define a discrete and insular minority because all persons, if they live out their normal life spans, will experience it." She also emphasized that lawmakers never made any findings that age discrimination among state employers was a problem: "Congress failed to identify a widespread pattern of age discrimination by the states."

O'Connor added in the end that state workers who face discrimination have other avenues of seeking retribution. "State employees are protected by states' age discrimination statutes, and may recover money damages from their state employers, in almost every state of the union."

Some employment lawyers said the court's rationale could have ramifications in other anti-discrimination cases because, in determining whether Congress could override states' 11th Amendment immunity, the court drew a line between characteristics that have robust constitutional protection and all others.

The Americans With Disabilities Act includes a similar provision for federal lawsuits against state employers who discriminate on the job and in state services. But the justices have accorded age and disability a lesser degree of constitutional protection than race and sex bias claims.

"This should be of grave concern," said Georgetown University law professor Chai Feldblum, who helped draft the ADA. "The question is whether there is enough evidence of state discrimination in the record [for example] of state police departments not handling deaf people, the mentally retarded, very well. It is a close question."