I once asked a criminal lawyer what he would do if, while defending a murder suspect, his client confessed. His duty was clear, the lawyer said. He would proceed with his defense but not, for fear of hearing perjured testimony, call his client to the stand. Those were his ethical obligations.

Journalists have their ethical obligations also. One of these is to honor confidentiality agreements. Aside from lying and plagiarism, there is probably no higher journalistic sin than revealing the identity of a person who, on the promise of confidentiality, supplied information. Those are the rules.

Because of those rules, I could not go around The Post's newsroom and ask my colleagues who leaked the tape of Mayor Marion Barry allegedly using cocaine in the Vista Hotel last January. That tape is exhibit No. 1 in the government's case against Barry. It purportedly shows the mayor having a drink or two, using drugs and making a pass at Rasheeda Moore, a former girlfriend the government used to lure the mayor to the hotel room.

But the tape also has its uses to the defense. It may show Moore taunting Barry to take drugs. She purportedly uttered the word "chicken," although that's not at all clear at this point. What is clear is that if she dared the mayor to take drugs, if she suggested that drug use was a precondition to having sex, then Barry might not seem the inveterate drug user the government alleges but merely a man who lost his better judgment on the way to losing his judgment entirely. In a different room, this is what happened to Sampson.

The Post has published several stories filled with details about what purportedly is on the tape, even including lengthy quotations from it. A copy of the tape also has been reported to be in the possession of WRC-TV. The question -- or at least a question -- is who leaked it. In a radio interview, Barry said the prosecution did. He charged that leaking the tape was part of a government effort to drive him from office. It fits neatly in the greater charge that this black mayor is being persecuted by the "white establishment."

But what if the government had not leaked the tape? What if either the actual tape or a detailed description of it was leaked by the Barry camp in an effort to discredit the prosecution? In fact, I have been told -- and not by a colleague, either -- that it was not the government that leaked the tape. It's reasonable to assume then (although I cannot prove it) that the tape came from the Barry camp.

Some things need to be said right here. The first is that Barry might not have known when he made the charge that the government was not responsible for leaking the tape to the news media. The second is that either he or someone on his defense team by now knows the truth. By letting the charge stand, he only exacerbates the racial division in this town, further fanning the suspicions of some blacks that the ubiquitous "they" is out to get the black mayor. "They" in this case is every institution from this newspaper to the U.S. attorney's office.

Well, I am already on record as being troubled by a sting operation, especially one that capped a mighty investigative effort and that resulted in nothing more than possession and perjury charges. Those charges are serious, but they are not in the same league as municipal corruption. But if the prosecution was too zealous in its investigation of Barry, the mayor's insistence -- either stated or suggested -- that he is the victim of racial injustice is even more troubling. By his own admission, he used illegal drugs.

Only in the strictest terms is the Barry case a legal one. Both the government and the defense have used the press. The government at first seemed to offer a deal: resign as mayor, and we'll accept a plea to a lesser charge. Now it may be the defense that's seeking a deal. The mayor has suggested that the government launched a vendetta against him -- and for racial reasons, some of his supporters add. A jury will have to be selected -- one that will, the mayor insists, fail to convict him. In a town that's overwhelmingly black, the mayor seems to think he has the perfect defense: he too is black.

In recent stories, The Post and other news organizations have reported information to put in doubt the mayor's version of who leaked the tapes. Given this newspapers rules, and given that I once was prepared to go to jail rather than reveal my sources to then-vice president Spiro T. Agnew, I am not about to ask colleagues to do what I would never do. I respect their professionalism. It's the professionalism of those who would leak information and then point a finger at someone else that all of us have to worry about.