AT THE REQUEST of the U.S. Court of Appeals here the Justice Department has filed a brief in a case testing the constitutionality of the 1978 Ethics in Government Act. That act allows the appointment, ultimately by the judicial branch, of special prosecutors or independent counsel to investigate cases of alleged wrongdoing by high executive branch officials. Normally prosecutors are themselves executive branch officials, but the thought is that, above a certain level, the executive branch should not be expected to investigate itself. The constitutionality of the statute has never been tested because, until recently, no such investigation had ever produced an indictment.

Department officials said in the brief that they were reluctant to advance their views in light of "our appreciation and endorsement of the policy objectives served by the Independent Counsel statute." But their views have long been known and come as no surprise. These officials believe the law is an unconstitutional breach of the separation of powers.

The administration is not alone in this opinion. Former attorney general Edward Levi opposed a law of this kind in testimony before Congress in 1976. Former attorney general Griffin Bell, who originally favored enactment, has now suggested that the law be allowed to expire. Nor is the administration doing as it did in seeking reversal of the abortion decision, Roe v. Wade. It is not persisting for political reasons or reasons of show in asking the courts to undo what they have just done; they have not ruled here.

Provision has also been made so as not to disrupt the work of the record number of independent counsel now appointed. All have been offered parallel appointments as Justice Department prosecutors so that if the law is struck down they can continue their investigations as special executive branch employees. Some have accepted the double designation and others, believing it undermines their independent status, have not. The offers remain open.

But give the administration all this; it still takes the wrong position. The very fact that its motives can be so easily misunderstood suggests why. The attorney general keeps a role in the present process. He must activate it by asking judges to appoint a special prosecutor. After that the case is taken largely out of his hands because it is a conflict of interest to have an administration investigate itself. For credibility's sake it has to be separately done; here the separation is careful as can be. The law is not being abused, and is doing the country much more good than harm. It ought to be upheld.