Supporters of Washington Mayor Marion Barry are like fans of an outclassed local boxing favorite. They are watching their man, apparently defenseless, get hit with blow after telling blow. Victory seems out of the question. Their only hope is for an outrageously biased hometown decision or a disqualifying foul from the other guy.

It's true that the defense is yet to be heard from, save on cross-examination. But each day's testimony makes it more difficult to imagine that the embattled mayor can have enough in reserve for a late-round comeback.

Hope is dead that the videotapes of that fateful night in the Vista Hotel might prove sufficiently fuzzy or ambiguous to obviate their impact. Maybe Rasheeda Moore went too far in urging her one-time lover to smoke crack, but there can be no doubt that he smoked it. He might have been the victim of a setup, as the defense alleges, but he was not the victim of a frame-up, and there is a world of difference between the two.

No sane viewer of the tapes can believe that the mayor was smoking Luckies, or that the man on the TV monitor was an actor pretending to be Barry or that Moore's words of encouragement were enough to tempt a rational man into a first-time use of cocaine. This, after all, was no weak-willed schoolboy giving in to peer pressure on the playground. This was a self-described "strong" black man, fully aware that the feds were after him and insistent that he was too smart to be tempted into using dangerous drugs. His videotaped actions and words give the lie to his contention that he had never used drugs or been knowingly in the presence of those who did.

But if the tapes were a major blow to his credibility, the rain of punches from a succession of witnesses saying that they had done drugs together has him reeling. The restaurateur who said he and "Mr. Mayor" used cocaine and opium on numerous occasions; the former girlfriends who described his "M. B. special" of cocaine in tobacco or marijuana cigarettes the lawyer who recounted the 1987 Super Bowl party at which he smoked marijuana with Barry before Barry disappeared into a bedroom with a woman and later had to be hospitalized for a "hiatal hernia," which looked suspiciously like a drug overdose -- all were staggering blows.

Their testimony is tainted, of course, by the fact that they, like Charles Lewis, who previously had testified that he and Barry smoked crack at the Ramada Inn, are themselves charged with crimes and were testifying as part of a deal they made with the prosecutor. But the nature of the charges against Barry almost precludes the possibility of an innocent witness, and the damning tapes give credence to the testimony.

Indeed, the wonder is that Barry would choose to fight, given his knowledge of what was on the tapes and the nature of testimony likely to be adduced against him. Wouldn't it have been better for him, and infinitely better for his traumatized city, to have recognized his virtual defenselessness and stayed out of the ring?

The thought of making a clean breast of things apparently never crossed Barry's mind. His initial strategy was to attack the prosecutor who brought the charges and the media that reported them, next to paint himself as a victim of racist prosecutors who couldn't stand the idea of a "strong" black man holding public office, and then, in desperation, to volunteer for treatment -- not for narcotics abuse but for "alcoholism."

And what now? It's foolhardy to underestimate the survival ability of the street-fighter mayor or the resourcefulness of his lead lawyer, R. Kenneth Mundy. Who knows what legal traps may already have been laid, or what surprise testimony will be presented or what reasonable doubt may yet be cast on the seemingly overwhelming evidence heard and seen so far.

But to this fight fan, the only realistic hopes seem to be that either the trial or an appellate court will rule the Vista Hotel bust a disqualifying "foul" or that at least one member of the jury will refuse to admit that the local guy lost the fight.

That may be enough to keep the mayor out of jail. But it will hardly qualify as a victory -- either for Barry or for the city that is already paying the price for his insufferable and arrogant behavior.