WASHINGTON — The Supreme Court ruled Monday that white firefighters in New Haven, Conn., were unfairly denied promotions because of their race, reversing a decision that high court nominee Sonia Sotomayor endorsed as an appeals court judge.

The ruling could alter employment practices nationwide and make it harder to prove discrimination when there is no evidence it was intentional.

New Haven was wrong to scrap a promotion exam because no blacks and only two Hispanic firefighters were likely to be made lieutenants or captains based on the results, the court said Monday in a 5-4 decision. The city said that it had acted to avoid a lawsuit from minorities.

The ruling could give Sotomayor’s critics fresh ammunition two weeks before her Senate confirmation hearing. Conservatives say it shows she is a judicial activist who lets her own feelings color her decisions. On the other hand, liberal allies say her stance in the case demonstrates her restraint and unwillingness to go beyond established precedents.

Coincidentally, the court may have given a boost to calls for quick action on her nomination.

The court said it will return Sept. 9 to hear a second round of arguments in a campaign finance case, and with Justice David Souter retiring there would be only eight justices unless Sotomayor has been confirmed by then.

In Monday’s ruling, Justice Anthony Kennedy said, “Fear of litigation alone cannot justify an employer’s reliance on race to the detriment of individuals who passed the examinations and qualified for promotions.” He was joined in the majority by Chief Justice John Roberts and Justices Samuel Alito, Antonin Scalia and Clarence Thomas.

In dissent, Justice Ruth Bader Ginsburg said the white firefighters “understandably attract this court’s sympathy. But they had no vested right to promotion. Nor have other persons received promotions in preference to them.”

Justices Souter, Stephen Breyer and John Paul Stevens signed onto Ginsburg’s dissent, which she read aloud in court Monday. Speaking dismissively of the majority opinion, she predicted the court’s ruling “will not have staying power.”

Kennedy’s opinion made only passing reference to the work of Sotomayor and the other two judges on the 2nd U.S. Circuit Court of Appeals who upheld a lower court ruling in favor of New Haven.

Sen. Patrick Leahy, chairman of the Judiciary Committee, said Sotomayor should not be criticized for the unsigned appeals court decision, which he asserted she did not write. “Judge Sotomayor and the lower court panel did what judges are supposed to do, they followed precedent,” said the Vermont Democrat who will preside over Sotomayor’s confirmation hearings next month.

In New Haven, Nancy Ricci, whose son, Frank, was the lead plaintiff on the lawsuit, carried a large cake decorated with red, white and blue frosting into the law office where the firefighters were celebrating their victory.

The ruling is a sign that individual achievement should not take a back seat to race or ethnicity,” said Karen Torre, the firefighters’ attorney. “I think the import of the decision is that cities cannot bow to politics and pressure and lobbying by special interest groups or act to achieve racial quotas.”

At a press conference in New Haven, firefighter Frank Ricci said the ruling showed that “if you work hard, you can succeed in America.”