The Justice Department waded into the "comparable-worth" debate for the first time yesterday, arguing in a legal brief that appropriate salaries for men and women should not be determined by "subjective judicial analysis."

In a friend-of-the-court brief filed with the 7th U.S. Circuit Court of Appeals in Chicago, the department sided with the state of Illinois in a suit filed by the American Nurses Association.

William Bradford Reynolds, assistant attorney general for civil rights, argued in the brief that judges should not be given power to decide how different people should be compensated for different jobs.

"Congress recognized that the judiciary was ill-equipped to perform such a task and that any such effort would inevitably result in unwarranted interference with legitimate management prerogatives . . . ," the brief said.

The Reagan administration has repeatedly criticized the argument that jobs dominated by women are underpaid because of sex discrimination and that wages for such jobs ought to be raised to match those of men holding jobs of comparable skill and experience.

The nurses' group is seeking monetary damages, citing a state study that purportedly showed lower wages for "female-dominated sex-segregated job classifications." A U.S. District Court judge dismissed the nurses' suit in April, ruling that there was no basis in law for their claim of wage discrimination. The appeals court must decide whether to uphold that ruling or order a trial.

Reynolds' brief said only one of the allegations, that nurses are not receiving equal pay for equal work, should be tested at trial. It said the plaintiffs' other allegations are based on "a theory of comparable worth requiring the District Court to embark on a course of subjective judicial analysis of the inherent worth of state employment positions . . . ."

Reynolds added in a statement that comparable worth "makes a mockery of the ideal of pay equity . . . . This approach would necessarily lead to a massive restructuring of our nation's economy and install the federal judiciary as a 'central planning commission' that establishes 'proper' wages for virtually every employer . . . ."

A number of states and cities have grappled with the issue in response to studies showing that an average woman with four years of college can expect to earn about the same salary as a man who never finished high school.

U.S. Civil Rights Commission Chairman Clarence M. Pendleton has denounced the concept as "probably the looniest idea since 'Looney Tunes.' " And President Reagan recently called comparable worth "a cockamamie idea . . . [that] would destroy the basis of free enterprise."

The Equal Employment Opportunity Commission said in June that it would reject cases based on comparable worth as a form of job discrimination.