The Supreme Court apparently has sprung another leak. Elizabeth Olson, United Press International's correspondent at the court, said yesterday that she has obtained an advance copy of an opinion and will file a story on it for release tomorrow.

Ordinarily, opinions are secret until the moment the justices announce them from the bench. Several leaks in recent years touched off hunts for the sources and a major controversy about security at the court.

Olson said she has obtained the court's ruling in a highly publicized case. The County of Washington v. Alberta Gunther. It addresses the issue of "comparable worth" -- whether federal sex-discrimination laws can be invoked when women are paid less than men for jobs that are similar, but not exactly the same.

Four former jail matrons in Oregon alleged that they received lower pay for guarding female prisoners than did male employes who guarded male prisoners. The county said that the jobs were not equal and that the Civil Rights Act of 1964 could not be invoked unless there was unequal pay for equal jobs.

Special precaution is taken by the Supreme Court to avoid leaks, not only as a matter of tradition but because leaks of rulings on business cases could influence the stock market or investment decisions. Some cases involve millions of dollars in potential gain or loss for corporations. In addition, the justices can change their minds on a decision up until the very last moment it is announced.

Olson declined to describe the opinion and would not say how she obtained it. But she said she had no doubt about its authenticity.

Olson, who has covered the Supreme Court for three years, said she gave "serious thought" to the authenticity of the material she has obtained and to the propriety of releasing the story.