WE PUBLISH today a second letter from Marine Corps Col. M. E. Rich concerning a recent editorial on the Moscow Marine guards case. Col. Rich suggests that the dismissal of charges against some of the Marines initially implicated is not an indication of their innocence or of serious mistakes made by investigators. He says, quite simply, these are difficult cases and that we shouldn't press too hard or too quickly for explanations. Gen. P. X. Kelley, the retiring commandant of the Marine Corps, was much more aggressive in his denunciation of the press on "Face the Nation" last Sunday. His statement, implying that questioners are somehow showing disrespect for the nation's war heroes, is preposterous -- and also doesn't answer the question. "Since 1976," he said "there have been 56 specific cases of espionage in this country that have been documented by the defense investigative service, and in no instance . . . was the organization taken on as a culprit. It was the individuals, and recognized as such. . . . I don't criticize the press for taking on the Corps as an institution . . . it's the manner in which they did it, using the Iwo Jima statue where we had almost 8,000 Marines 40 years ago who gave their lives for their country. To use that as a gimmick was just a little beyond, I think, what I consider to be responsible journalism."

This is boilerplate. Seeking information about events that were billed as a national security scandal of the first order has nothing to do with feelings about the Marine Corps, about "taking it on." Most Corps veterans, we would think, would be the first to want to get to the bottom of this case, either to punish the few men who have abused the uniform or to exonerate them, depending on the facts. Of course, these are difficult cases -- if they are cases at all -- but so are most espionage prosecutions. The question is whether they have been made even more difficult because they were handled improperly from the start. As is the case in any criminal court, an unsubstantiated confession where there is no evidence that a crime has even been committed will not result in charges. Investigators have to go out and look for the body, the fingerprints or the broken window. In this case, questions have been raised about how this job was done since absolutely no physical evidence of a crime was produced. Some of the Marines have also charged that their confessions were obtained after days of harassing questioning in an isolated motel room, that they were threatened and that they were not properly advised of their rights. The agency that conducted the investigation is a recently reorganized civilian arm of the Navy, and at least one congressman has charged that it was simply not up to the job.

If military and civilian authorities think that espionage was committed but that those who did it cannot be prosecuted because of the difficulty of getting the required information "in an unfriendly country," as Col. Rich says, then this surely mandates some further security precautions in our embassies in such countries, precautions that evidently are not now being taken. If the case was bungled by investigators, that should be admitted, and some other system for pursuing espionage cases within the military should be devised. And if there was no espionage in the first place, the names of these young men should be cleared at least of this heavy charge. Nothing can be done, though, until all the facts are made public. The Marines and their supporters everywhere must surely see the wisdom of speeding the process