A federal judge rejected claims yesterday that the State Department discriminates against women in the Foreign Service and said the department "should be commended" for making "every reasonable effort to remove any vestiges of sexual discrimination" from its operations.

The 50-page opinion by U.S. District Court Judge John Lewis Smith Jr. follows a month-long trial last spring in which plaintiffs said the department shunted women into less prestigious jobs and gave them fewer promotions than men.

Smith said he found no evidence of "disparate treatment" in job assignments, promotions and evaluations.

Although proportionately fewer women hold the department's top posts of ambassador and deputy chief of mission, Smith said the discrepancy does not show discrimination within the last decade because of "the time necessary for the large number of female FSOs presently in the service to advance to the higher ranks."

The lawsuit, filed in 1976, also accused the department of sex discrimination in hiring. Under a consent decree two years ago, the department agreed that some of the women would be allowed a second chance to qualify for the foreign service, but no changes were required in future examination practices.

Smith accepted evidence that proportionately more women have been assigned to consular posts than areas of political specialization but said this reflected their preferences. "No credible testimony was offered that any female FSO has been assigned because of sexual discrimination," he said.