When R. Kenneth Mundy acknowledged yesterday for the first time publicly that D.C. Mayor Marion Barry had been an occasional cocaine user, he took an almost unavoidable risk that could permit the jury to convict on at least one misdemeanor charge.

But Mundy's acknowledgement also allowed him to remind the jury that occasional cocaine use was not the issue in the trial; that their job will be to decide whether specific charges -- pinpointed to specific dates -- have been proved beyond a reasonable doubt.

"We do not mean for one moment to give you the impression that there was not a use of cocaine, occasional use of cocaine by Mr. Barry during the period in time that we have evidence about, but I also want to tell you that that is not what the case is about."

"Except for the conspiracy charge," Mundy told the jury, Barry "is being charged with specific instances of alleged misconduct, and in order for you to convict him you must be satisfied beyond a reasonable doubt of his misconduct as alleged specifically by the government in the indictment."

Mundy's tactic was risky, defense lawyers said yesterday, but probably his only option given the parade of close Barry associates who testified they used drugs with the mayor.

"He's got a boatload of evidence that he's got to deal with," said William Pease, a criminal defense lawyer and former prosecutor. "He knows that he cannot simply say that all these people are all lying about everything and that Barry is not a drug user . . . . For him to say otherwise would insult their intelligence and would essentially reduce any credibility for any legitimate arguments that he has."

Such a tactic -- admitting something small in order to beat the bulk of the charges -- is common among defense lawyers. "The only way to win it is to fess up sometimes," said defense lawyer G. Allen Dale.

To do otherwise could risk losing the jury altogether. "The jury would turn away," Dale said. "If they think you, as an attorney, are not being honest, they are not going to listen to you."

The public confession to illegal drug use -- dispensed in the first few minutes of his closing statement -- also was a tacit admission that Barry's political future is taking a back seat to his legal troubles.

Other than an acknowledgement this year in a media interview that he had used crack cocaine at the Vista Hotel during the undercover sting, Barry steadfastly has insisted that his was an alcohol and prescription drug problem.

"Nor do we mean to indicate that there was not some type of conduct that was not popular or not appropriate," Mundy told jurors yesterday. "But, ladies and gentlemen, you sit in a jury box, you don't sit in a ballot box.

"You are performing a service now as jurors, not as voters, and it is not whether you like Mr. Barry, whether you like Mr. Barry's lifestyle or whether you like things that have been paraded here about Mr. Barry . . . . The question is whether the government has proven guilty beyond a reasonable doubt."

Outside the courthouse, Robert W. Mance, Barry's other attorney, said Barry had been "very receptive" to publicly stating he was a drug user.

Mundy will continue his closing statement today, but he sent the jurors home with two clear messages to sleep on: that this was essentially a misdemeanor case hung around a few felony perjury charges and that the government had mounted an unfair attack that transcends Barry in its implications.

Comparing the marshalling of government forces against Barry to the use of mustard gas in war, Mundy said: "Our society is a society of laws, and even those who seek to enforce the laws are governed by certain responsibilities . . . . It might be Mr. Barry today and somebody else tomorrow."