AMONG THE last-minute legacies of the Carter administration, none strikes us as more troublesome than the consent decree signed last week by the Justice Department (over the objections of the Reagan transition team) assuring minorities a higher portion of professional jobs in the federal government. The aim of the decree is good. The method is bad, demeaning to everyone involved.

Under the terms of the agreement, the government would stop using the Professional and Career Entrance (PACE) exam to qualify applicants for entry-level professional jobs. Instead, agencies would experiment with other ways of screening applicants to find one that would ensure that a required number of applicants from each major racial and ethnic group are found to be qualified. The quotas to be filled (although the Justice Department argues that they are not quotas) would be determined by an earlier regulatory requirement that passing rates for whites, blacks and Hispanics be roughly equal. For example, if 40 percent of whites were found to be qualified, then about 40 percent of blacks and Hispanics would also pass. Currently, only 5 percent of blacks and 13 percent of Hispanics pass the PACE exam, compared with 42 percent of whites.

Part of the trouble with the proposed procedure comes from the earlier regulation that decided that a more or less uniform success rate for each group of applicants was a good indicator of whether or not a test was fair. But the consent decree makes matters even worse by enshrining the notion that it's all right to pretend that something is done on a competitive basis and then fudge the testing procedures so that in fact it is not.

When you corrupt the standards by which you recruit, you do more than corrupt the people who give the test and those who take it. You also undermine the morale and cheapen the accomplishments of all those who had been measured against the previous standard and passed. Judge Joyce Green of the U.S. District Court must now decide whether to approve the decee. We hope she will reject it.