WASHINGTON, June 9 ? A unanimous Supreme Court made it significantly easier today for workers to win discrimination suits against their employers in cases where race, sex, religion or national origin is one factor among others in a dismissal or other adverse job action.

Such cases of "mixed motive" ? a legitimate reason combined with an improper, discriminatory one ? are so common as to be the norm in the world of employment discrimination litigation. Congress addressed this category of cases, among others, in 1991 when it amended Title VII of the Civil Rights Act of 1964, the basic federal employment discrimination law, to counter a series of pro-employer Supreme Court decisions.

A 1989 Supreme Court ruling had made it difficult for plaintiffs to qualify for the favorable jury instructions that come with a mixed-motive case, under which the employer has the burden of proving that it would have made the same decision even in the absence of the improper factor. The court said then that the plaintiff must prove by direct, not circumstantial, evidence that discrimination had been "a motivating factor" in the employer's action.

Direct evidence requires the equivalent of a smoking gun. While it is sometimes available to aggrieved employees, it often is not, particularly in the nuanced and complex situations reflected in many mixed-motive cases.

In its 1991 legislation, Congress provided that an "unlawful employment practice is established" when the plaintiff "demonstrates" that race or any of the other prohibited categories "was a motivating factor for any employment practice, even though other factors also motivated the practice."

Although Congress made no mention of a need for direct evidence, the lower federal courts continued to require it, with the exception of the United States Court of Appeals for the Ninth Circuit, in San Francisco. In an opinion by Justice Clarence Thomas, the Supreme Court said today that the Ninth Circuit was correct.

"On its face," Justice Thomas said, "the statute does not mention, much less require, that a plaintiff make a heightened showing through direct evidence."

"Our precedents make clear," he added, "that the starting point for our analysis is the statutory text. And where, as here, the words of the statute are unambiguous, the judicial inquiry is complete."

Beyond the decision's impact on civil rights litigation, an effect that could be substantial, the case was notable for the court's unanimous rejection of the position argued by the Bush administration. The administration had urged the court to adhere to its direct-evidence requirement, arguing that Congress in 1991 intended to overturn other aspects of the 1989 decision, Price Waterhouse v. Hopkins, but not the evidentiary standard.

Justice Sandra Day O'Connor, who formulated the direct-evidence standard in her separate opinion in the 1989 case, wrote a concurring opinion today. She said that while she still believed that her original view accurately reflected what was then the state of the law, the result today correctly reflected the change that Congress made in 1991.

The case, Desert Palace v. Costa, No. 02-679, began as a suit against the management of Caesars Palace Hotel and Casino in Las Vegas by Catharina Costa, who worked there as a truck driver and heavy-equipment operator. Ms. Costa was the only woman to work in the hotel's warehouse. After she was dismissed, following a fight with another employee that management stated as a cause, she sued for sex discrimination and sexual harassment. The case was tried as a mixed-motive case, and Ms. Costa won a jury award of $364,000 for back pay and damages.

The hotel then appealed on the ground that in the absence of direct evidence, Ms. Costa was not entitled to the favorable mixed-motive jury instructions. Instead, the hotel said, she should have been required to meet a higher burden of proof by showing that the stated reason for her dismissal was a pretext for discrimination. A three-judge panel of the Ninth Circuit initially agreed, but a panel of 11 judges reheard the case and, departing from the uniform view of the other appeals courts, held that direct evidence was not necessary.

The unanimity of the ruling today, along with the fact that the appeals courts other than the Ninth Circuit were still requiring direct evidence, "illustrates how much more conservative the lower courts are these days than the Supreme Court," Eric Schnapper, a law professor at the University of Washington who helped represent Ms. Costa, said in an interview. He said that there were hundreds of similar cases in the pipeline and that plaintiffs would benefit from the lowered threshold the court set today.