Though it's normal for political appointees to quit during the last year of an administration, the resignation of six top officials at the U.S. Department of Justice is an unusually large and sudden exodus.

So unusual that it's easy to believe the six officials, who aren't talking publicly, resigned because Attorney General Edwin Meese won't step down despite his continuing and burgeoning troubles with the law. The fact that none of the six have other jobs lined up lends credence to such suspicions.In any event, the resignation of the six officials including the Justice Department's No. 2 man and its top criminal prosecutor leaves the department with a big void in its top leadership. In fact, none of the remaining assistant attorneys general have much experience in criminal law.

Moreover, the void could get worse; other Justice Department aides are said to be seriously considering following their six former colleagues out the front door.

The prospect, then, is for morale and efficiency at the Justice Department to drop below their already abysmally low levels.

Under other circumstances, the sudden departure of so many top aides might argue for Ed Meese to stay on as attorney general in the face of increasing calls for his resignation, including calls from some of President Reagan's staunchest friends and admirers, who understandably see Meese as a political liability.

As it is, however, if Meese did step down, he likely wouldn't be missed. Meese must spend such an inordinate amount of time defending himself, that many of his duties have been delegated to subordinates.

From the outset, Meese has been in trouble repeatedly. Since his confirmation as attorney general in 1985, he has been investigated by three special prosecutors and the Office of Government Ethics. Though he has managed to emerge largely unscathed so far, his previous brushes with controversy weren't nearly as serious as the shadow under which he now finds himself.

Currently, a special prosecutor has been investigating Meese's role in an Iraqi oil pipeline project, his ties to the scandal-plagued Wedtech Corp., and his financial affairs. A decision on whether or not to bring criminal charges against him is expected soon. His activities also have come under investigation in Congress. With the departure of some of Meese's closest subordinates, the continuing attacks on him can no longer be dismissed as just partisan politics.

Like any other American, the nation's top law enforcement official ought to be presumed innocent until proven guilty. But the presumption of innocence applies only as far as it is needed to assure the law is executed fairly; it is not a standard for determining fitness for a Cabinet post.

Rather, the attorney general ought to be above suspicion, particularly in an administration that prides itself on being tough on crime. Ed Meese, however, is constantly under suspicion and constantly must spend time defending himself time that ought to be spent pursuing drug dealers and other criminals.

In many respects, Ed Meese has served the nation well, particularly when it comes to such things as his vigorous fight against pornography. But the nation and the White House are not served well when controversy over a particular public servant goes so far that it leaves the government with a major department crippled. Sometimes an official also serves the public by knowing when to leave.