The prosecution has rested in the case of Marion Barry, and we now can watch the defense. But in the case against crack, the verdict is already in. Variously touted as a killer-drug, a violence-inducer and so addictive that one hit and a mad craving for life surely follows, it has to be found not guilty as charged. It's just another drug.

And just another lie. The lie, of course, was that crack was something new under the sun -- a drug so powerfully addictive that it brought almost instant ruination. From time to time, a vain voice was raised in objection, but it was invariably hushed lest, I guess, kids get the wrong idea.

We now have Marion Barry to prove otherwise. The mayor used crack -- so says he, a bevy of witnesses and, of course, those famous videotapes. Certain witnesses allege Barry ran into some difficulties with drugs and nearly overdosed at least once. But if the videotapes prove the mayor used crack, they also prove something else: the man the FBI arrested was neither violent nor in a stupor.

For all of Barry's alleged drug use, he nevertheless functioned as Washington's mayor. He did his job -- more or less. At times he had trouble getting up in the morning, but then so does anyone who has had a few too many drinks the night before. Whatever the ill-effects of his crack usage, this much is clear: Barry did not become a violent, raving maniac. Seen by countless numbers of people daily, it ultimately took a government sting operation to reveal him as a drug user.

This is not a column advocating the use of crack (or any drug) or suggesting that such usage cannot have awful consequences. It is a column, though, that once again accuses the government and the media of lying to kids. Repeatedly, government and law enforcement officials have made the most absurd statements about crack, and the media, out of a sense of civic responsibility, have printed them without any rebuttal. The result, I suggest, is what in the Vietnam War era was called a credibility gap.

At long last, it seems that the so-called War on Drugs has turned a corner. Surveys report less and less drug consumption, and emergency rooms report fewer overdoses. All of this is good news -- but not unexpected. The nation has had drug epidemics before. They wax and wane, seemingly of their own accord.

What happens is this: eventually people wise up about drugs and avoid them. It's almost inconceivable now, for instance, that a rock group could extol the use of a drug -- any drug -- in a song. In the 1960s, though, that was routine. The diamonds that Lucy saw in the Beatles' sky were almost certainly LSD.

When the conventional wisdom about drugs goes from acceptance to rejection, it's because people have finally recognized the truth. But when the government exaggerates the dangers of drugs, it loses its credibility. Tell a kid that marijuana use will lead inexorably to harder drugs, and he scoffs. After all, he knows oodles of people who used the former but not the latter. Tell him crack is an instant killer, and he scoffs some more. He simply knows better.

But these are precisely the messages the government and a compliant media sent to kids. They listened -- and disbelieved. Worse, they figured that if they were being lied to about specifics, then they were being lied to in general. Probably the lie about marijuana accounted for more experimentation with and, in some cases, addiction to harder drugs than the power of marijuana itself. People who progressed from one drug to the next had logic on their side. If they had been lied to about marijuana, why should they assume they were being told the truth about cocaine?

The dangers of drugs are real enough without having to exaggerate them -- but exaggeration has been the rule. When, last year, Jefferson Morley described in The New Republic how he had used crack once and not become addicted, he was roundly denounced by both government officials ("irresponsible," said William Bennett) and protectors of the public morality in the media. The same reception awaited anyone who veered from orthodoxy, including Ethan Nadelmann, the legalization advocate from Princeton. Everyone was agreed: crack was instantly addictive and violence-inducing. You can look it up.

Those of us who have followed Marion Barry would be hard-pressed to say how drugs changed him. Crack might have worsened matters, but so might another drug, including booze -- a drug that certainly can induce violence and to which countless numbers of people are addicted. In a way, the trial of Barry has also become a trial of the government's and the media's credibility on drugs. It's not too late to cop a plea: incompetence.