RECENT PUBLIC comments by the former counterintelligence chief of the Los Alamos National Laboratory, Robert Vrooman, further muddy the waters of the scandal surrounding Chinese espionage at American nuclear labs. Mr. Vrooman told Post staff writer Vernon Loeb that Wen Ho Lee, the former Los Alamos nuclear scientist who came under suspicion for espionage, was suspected largely for ethnic reasons. He said that the case was "built on thin air" and that the information Mr. Lee was suspected of compromising -- the design of the W-88 nuclear warhead -- had been disseminated to private contractors and "hundreds of locations throughout the U.S. government." The Energy Department has recommended disciplinary actions against Mr. Vrooman for alleged missteps in the Lee probe, so he is not exactly an unbiased figure. But his remarks emphasize the need for caution when discussing Mr. Lee -- who is, after all, an American citizen charged with no crime -- and the nuclear espionage issue in general.

The public has no access to the actual evidence about Chinese nuclear espionage, which is overwhelmingly classified. This secrecy may be proper, but it puts the public in the position of choosing between summaries of the evidence that are not fully consistent with one another.

All the groups that have examined the evidence agree both that there were significant security lapses at the labs and that China has somehow obtained through espionage design information about American warheads. These are deeply disturbing revelations whose seriousness is unaffected by whatever may be the rest of the truth in the matter.

There is, however, no agreement about the extent of the weapons information the Chinese obtained, how they obtained it or the degree to which they have incorporated American technology into their own weapons. The bipartisan Cox committee concluded that the penetration of the labs was deep and that the information "stolen" contributed greatly to the Chinese nuclear weapons program. The public summary of the CIA's own damage assessment concurs that serious disclosures took place that probably accelerated Chinese weapons development, but it also said that the investigative panel could not determine how important a factor espionage was in Chinese weapons development and that "the aggressive Chinese collection effort has not resulted in any apparent modernization of their deployed strategic force or any new nuclear weapons development." The administration, meanwhile, has gone through a succession of defenses mainly meant to shift the blame to past administrations while also claiming to have moved aggressively to fix security problems. It's hard to take these relentlessly self-serving statements at face value.

All of which makes it very difficult to know what to think of Mr. Lee -- especially in light of mounting evidence that the case against him was thin from the beginning. Mr. Lee, according to information released by the Senate Governmental Affairs Committee, came under suspicion because he was working at Los Alamos between 1984 and 1988, had access to the W-88 information, had been to China, received visiting Chinese delegations and had fallen under FBI scrutiny before. There seems never to have been any direct evidence that he compromised the W-88 information or passed material to the Chinese. Moreover, if Mr. Vrooman is right that many people outside Los Alamos had access to the W-88 design, investigators' focus on the lab as the source of the leak may have identified an unnaturally narrow cohort of possible suspects.

This is not to contend that Mr. Lee is innocent -- something we simply cannot know. But it is worth emphasizing that he is entitled to a presumption of innocence that he has not typically received in public discussions of the matter. More generally, the murkiness of this entire subject begs for a caution that has not so far been a feature of the commentary. The Lee case, for example, has been cited as evidence of the need to relax civil liberties protections to make surveillance easier in national security cases. This is a dreadful idea. At the same time, the larger problem of security lapses and espionage does not go away if Mr. Lee is not a spy, nor does the need for greater vigilance, and not just at the labs. That's true whether or not we learn any time soon what the exact extent of the Chinese nuclear espionage was -- or is.