Even in a business that cultivates and depends on leaks, one is inclined to say: enough.

Someone obviously close to the office of U.S. Attorney Joseph E. diGenova has been leaking word about an investigation involving Mayor Marion Barry. On the record, the city's federal prosecutor isn't saying anything at all.

But last week The New York Times printed a story saying a grand jury has received information contradicting the mayor's denial before the same panel that he purchased illegal drugs. The story said the grand jury "is now examning whether (Barry) committed perjury."

Early reaction to the reports on Barry was to the effect that where there is that much smoke, there must be at least a little fire. The reaction now, at least in some quarters (including this one) is that diGenova ought to put up -- get the federal grand jury to hand up an indictment -- or shut up. If he's got a case against Barry, let him put it on.

The suspicion is that he hasn't. That isn't to say that there is nothing to all this. After all, Barry has acknowledged having been involved in a "personal relationship" with a city employee who has been convicted and sentenced after pleading guilty to charges of possessing and conspiring to sell cocaine and who is now serving a contempt sentence for refusing to answer questions before the grand jury. In addition, his honor has managed to get himself into just enough situations to sow doubts among some as to his personal discretion.

But indiscretion is not an indictable offense. Drug use, which is, is an excruciatingly difficult thing to prove, in the absence of actual drugs. One indication of the difficulty is the latest leak published last week in The Times, that the grand jury is examining whether the mayor committed perjury, apparently by denying what diGenova has been unable to prove.

It is a quirk of the law that a perjury conviction, which requires only that a jury believe witnesses who claim to know that the mayor is lying, may be easier to secure than a drug-abuse conviction, which requires physical evidence; and that the personal use of drugs is only a misdemeanor, while lying about it to a grand jury is a felony punishable by up to five years in prison.

But the guess here is that an attempt to indict Barry for perjury would do more damage to diGenova's credibility than to Barry's, suggesting, as it inevitably would, that the prosecutor had been unable to make the case he has labored so mightily to make.

Already Barry is making some headway in his attempt to paint leaks from the prosecutor's office as an attempt to "lynch" him. And if lynching is defined as the summary punishment of suspects -- regardless of guilt -- without a trial, Barry has a case.

The problem with Barry is that he has never fully understood that a person in his position has no truly "private" life, outside his own home, and that, both as mayor and as role model for young people who look up to him, he has an obligation to carry himself more circumspectly now than when he was a street-smart civil rights advocate. Whether he ever used illicit drugs or not, one hopes that he finally has learned the value of discretion.

But indiscretion is not a crime. And my opinion is that unless diGenova has the basis for charging Barry with a crime, he ought to leave him alone.

Some conspiracy-minded Washingtonians are starting to believe that the effort to get Barry, whether in the courts or in the press, is political: an attempt to "rescue" the local government from black control. (If the mayor were removed from office, D.C. Council Chairman David Clarke, who is white, would become acting mayor.)

But even those who don't buy the conspiracy notion and who are prepared to believe the worst about Barry have problems with the pre-indictment trial-by-leak.

If they've got a case against the mayor, let them bring it. If they haven't, then they ought to leave the man alone.