Members of Congress violate the Constitution when they discriminate against women in their employment practices, the Fifth U.S. Circuit Court of Appeals ruled yesterday.

Unless overturned by the Supreme Court, the ruling will expose senators and representatives to personal liability and payment's of damages for job discrimination, for which they had been considered immune from any redress.

"Our Constitution protects individual rights, even against the mights," the New Orleans court said in ruling that former Rep. Otto E. Passman (D-La.) must defend against bias charges brought by Shirley Davis, whom he dismissed in 1974 as his administrative assistant in Monroe, La.

A U.S. District Court judge had dismissed the Davis suit but the appellate court, splitting 2 to 1, reinstated it, holding that is she proves her case, Passman violated her Fifth Amendment right to equal protection under the law.

Most experts on sex discrimination had considered such a sweeping constitutional victory highly unlikely. They conceded - and complained bitterly - that federal laws against sex discrimination did not bind Congress or its members.

But while the ruling gave women a new opportunity to sue, it did nothing to ease their burden of proof at trial. Passman, unlike most employers in sex bias disputes, wrote Davis a letter of dismissal that praised her work but flatly stated his preference for a man in the job.

"He put it in black and white," Davis, a widow with two grown children told Washington Post special correspondent Bill Lynch last night. Her lawyer, Stephen J. Katz of Monroe, said the judges expressed amazement from the bench that a public official would write such a letter.

Passman, a powerful congressman who served for 30 years, was defeated in the primary election last year, so he could not restore Davis to her $18,000-a-year job even if he wanted to. But the court held that her claim for damages and lost wages kept the case alive.

"Rep. Passman was free within constitutional limits, to dismis Davis at any time," the majority said, "but if the actual dismissal is found at trial to have been unconstitutional, then lost salary should be taken into account in assessing damages."

Passman's claim of immunity and his denial of discriminatory motive were both rejected by Chief Judge John R. Brown and Judge Irving L. Goldberg. Senior Judge Warren L. Jones dissented, accusing the majority of invading the exclusive domain of Congress.

"In this case," the majority said, "a member of the United States Congress unflinchingly asserts that the Constitution allows him openly to discriminate against women. Although representative admittedly have some insulation not wrapped around ordinary mortals, the conflicting interests must be harmonized, not dichotomized. Finding that our Constitution protects individual rights, even against the mighty, we remand this case for trial."

The court branded as "patently ridiculous" Passman's suggestion in his letter that the job called for a man because of its "diversity" and "unusually heavy workload." It said the qualifications for an administrative assistant simply have nothing to do with gender."

The court continued:

"Rep. Passman's contention that the constitutional ban on unjustified sex discrimination does not restrict the actions of members of Congress is equally untenable. He argues, in effect, that his congressional status endows him with an open-ended right to discriminate . . ."

Lawmakers enjoy immunity for legislative acts, the court noted, but not when they act outside the sphere of legitimate legislative activity.

The assumption that legislaters could not be held liable for sex discrimination has been widespread, despite angry reactions to last year's congressional sex scandals and charges that women had been cajoled into performing sexual favors in order to keep their jobs.

The Senate passed a resolution denouncing employment bias but provided no mechanism to handle complaints. Reps. Patricia Schroeder (D-Colo.) and Charles Rose (D-N.C.) organized a voluntary group to arbitrate complaints by House employees.

Passman was unavailable for comment last night as to whether his attorney would seek a rehearing before the full 15-member court of appeals or would petition the Supreme Court for review.