THE GREAT Marine spy scandal of last winter continues to recede. Now Staff Sgt. Robert Stufflebeam has been found guilty of two counts of dereliction of duty for having frequented off-limits bars in Moscow. He was wrong to do that, but it's hardly a sin that no Marine noncommissioned officer has ever committed before. He was lightly penalized.

The sergeant was accused in seven other counts of having had contact and sexual relations with Soviet women, having failed to report this and having lied about it. These charges, which still had nothing to do with espionage, were the more serious ones against him. The jury of five officers and three enlisted men acquitted him on all seven without his having even put on a defense. The quality of the evidence seems to have been part of the problem; a sense that, for reasons of its own, the Corps was making too much of his offenses may have been another.

No one is denying that there were problems within the Marine detachment at the Moscow embassy. At least one of them was serious. Marine Sgt. Clayton Lonetree, who was partly under Sgt. Stufflebeam's command, was convicted last month of having passed information to a Soviet woman who seduced him; he was sentenced to 30 years in prison. The great unanswered question is what else happened, whether this was all or there was more. Here we are dependent in part on the military investigative services to which the affair was entrusted. It is, to put it mildly, not completely clear they did a first-class job.

Thus the story at one point was that Marines had not merely traded secrets for sexual favors, as Sgt. Lonetree confessed to having done, but had allowed Soviet agents inside the embassy. That confession came from Marine Cpl. Arnold Bracy. It was a sensation. But then he recanted it and said Navy investigators had forced it from him. There was no supporting evidence, and charges against him were dropped. Was the story true or not? What seems from a distance to have been a hasty investigative process produced an unsatisfactory result.

So also here. Plainly Sgt. Stufflebeam broke the rules, some of which are important. But his transgressions had nothing to do with espionage; that was never even charged. Nor, even so, were most of them proved to the satisfaction of what might be expected to be a fairly stern jury. Something has to be done about the stationing and oversight of Marine guards at embassies in places such as Moscow. But surely something also should be done about the way affairs such as this are handled once discovered. And there is much more about these particular investigations that needs to be explained to the public.