A U.S. District Court judge has ruled that the federal Drug Enforcement Administration has discriminated against black special agents, including allowing "gross disparities" in salaries to exist.

In particular, Judge Aubrey E. Robinson Jr. found "overwhelming" evidence that black agents were assigned undercover work more frequently than white agents, assignments that adversely affected blacks by exposing them to greater danger and limiting their work experience.

Robinson noted that the DEA admitted that it made such assignments on the basis of race, and failed to come up with legitimate reasons for doing so.

THE DEA's "general and untested assumption that blacks must be used to make undercover buys from blacks does not justify" the discriminatory work assignments, Robinson said in a 49-page opinion.

DEA also admitted that blacks were more frequently and more severely disciplined than white special agents. Robinson also found that black agents were discriminated against in terms of employment promotions. He also ruled that DEA used subjective methods for making decisions about grade levels for entry jobs which had a disparate effect on black agents.

According to Robinson's written opinion, 138 of the 1,967 special agents employed by the Dea as of October 1978 are black.

The class action lawsuit, brought on grounds of alleged violations of Title VII of the Civil Rights Act of 1964, was heard at a trial before Robinson in April 1979. Contentions involving recruitment and hiring discrimination were settled before the trial.

Robinson's opinion in the case, issued last Friday, resolves only the question of liability on the part of the DEA in connection with race discrimination. Damage claims, including any award of back pay to black agents, will be handled in separate proceedings.

In an order that accompanied his written opinion in the case, Robinson told the DEA to submit proposals for remedying salary and promotion levels to the court by Feb. 27.

Robinson rejected the black agents contention that the DEA also had been discriminatory in its training procedures, and also dismissed a claim that black agents were harassed because of their efforts to promote equal employment opportunities at DEA.