Yesterday's accusation from the witness stand that D.C. Mayor Marion Barry had sex with Linda Creque Maynard against her will was the most dramatic sign to date that prosecutors are prepared to tar the mayor with suggestions of bad character and crimes not charged in his indictment.

That strategy is not unusual in high-stakes criminal trials, but it cannot be openly espoused. Federal rules of evidence and binding ethical canons forbid prosecutors from introducing evidence for the purpose of painting an unflattering portrait of the defendant. But there are many paths in a courtroom, and prosecutors have found ample opportunity to present Barry as a man of many sins.

Yesterday's testimony -- which evoked images of sexual assault, complete with sobbing victim on the witness stand -- was the most powerful example thus far of what lawyers call evidence of "other crimes." In previous days, however, prosecutors have imputed to Barry at least three additional crimes for which he has not been charged: distribution of drugs, possession of marijuana and a conspiracy to mislead a grand jury that sounded suspiciously like obstruction of justice.

Most pervasive of all, in the prosecution's evidence to date, has been the motif of sexual misconduct. Many of the witnesses have added detail to the government's portrayal of an oafish, groping womanizer. During some government questioning, the trial's central issues of drug use and perjury seemed almost secondary.

The government's target in all of this appears to be the sentiments of the jurors. Prosecutors are trying to cut their risk that some or all of the jurors will refuse to convict because they dislike the government's conduct more than the defendant's. Such a refusal to convict is known as jury nullification. Prosecutors, in effect, are trying to nullify the nullifiers.

"This is about character," said William D. Pease, a former senior supervisor in the U.S. Attorney's Office. "They {the prosecutors} are going after his character."

Experienced criminal strategists warn that the prosecution's methods are double-edged. The central theme of the mayor's defense is that the government will stop at nothing to destroy him, and prosecutors may fuel that story line as much as their own.

Defense attorney R. Kenneth Mundy already has charged the government with a conducting a vendetta against Barry, and such attempts could help him prove his point.

"When the government is on trial as much as the defendant is on trial, the government has to be very careful about walking a square corner," said another former criminal prosecutor.

Assistant U.S. Attorneys Richard W. Roberts and Judith E. Retchin set about from the beginning to combat Barry's advantage of position. Both have made a point of avoiding his title: witnesses may call him "the mayor," but to Retchin and Roberts he is always "the defendant" or "Mr. Barry."

Roberts set the stage for the sexual themes in his opening statement. Barry, he said, had a "torrid" relationship with Hazel Diane "Rasheeda" Moore, who cooperated with federal investigators to lure him to the Vista Hotel. And Roberts foreshadowed yesterday's testimony, telling jurors that Barry "tried to have his way with Ms. Maynard" in the Morning Star Beach Club hotel.

Succeeding days have included tidbits such as these:

Charles Lewis testified that Barry and Moore shared a hotel room and returned to it together to change into sailing clothes. Later, he testified that he left the mayor alone with Zenna Matthias because he didn't want to cramp the mayor's style.

Matthias said the mayor played a sexually explicit videotape, grabbed at her waist, invited her onto a bed and told her she was "conceited" when she declined. Lewis, Matthias said, mysteriously disappeared from the room.

Lewis and Matthias both testified that Barry drank "bullfoot soup," a reputed aphrodisiac on the islands.

Although prosecutors have elicited all the testimony about sex and sexual conduct, they also have gone out of their way to show that they are conforming to legal obligations.

Last Tuesday, the first day of testimony, Retchin asked for a bench conference to seek permission from the judge before eliciting from Lewis the testimony that another woman had performed oral sex on Barry on the beach. The judge said that evidence could wait.

"This is not just about marital fidelity," Pease said. "It goes much deeper than that. This is about maintaining the standard you espouse out on the street, on TV and the political stump . . . . When these other things come out to show you are a hypocrite . . . then they {jurors} may think you are not a decent person, and then you have a long way to go before they will find you not guilty."

Greta Van Susteren, a District defense lawyer who also teaches at Georgetown University Law Center, said testimony about sexual encounters shows "dishonesty with {Barry's} wife." If he is dishonest with one so close to him, Van Susteren said, the jury may believe he "was dishonest with the grand jurors, who he didn't even know."