The trial strategies of the prosecution and defense in the drug case of Mayor Marion Barry could emerge today as each side gets its first crack at the 250 District residents in the jury pool.

The tactics that have been rejected as unusable at trial could be just as important as the ones that find their way into the case.

Yesterday, as prospective jurors filled out questionnaires about their views and their backgrounds, lawyers on both sides were preparing to take their turn today questioning them about how they might decide the case.

For the prosecution, U.S. Attorney Jay B. Stephens will have to decide whether to treat this as he would any other drug case, or to accept that the Barry trial is special. If he does the latter, the object for prosecutors will be to portray Barry as a powerful man who squandered his fame and influence on drugs, women and a hedonistic lifestyle.

For the defense, it will be just as important to pound away at the theme of a government gone mad with the idea of dethroning a mayor, regardless of the time, energy and expense involved.

For U.S. District Judge Thomas Penfield Jackson, the challenge probably will be to retain control of a trial that could look more like body-checking in a hockey rink than a criminal case in federal court.

Defense lawyer R. Kenneth Mundy has said he will use neither an entrapment defense nor one based on Barry's acknowledged alcohol abuse. Both decisions apparently were made because the risks outweighed the advantages.

Entrapment is an effective defense only when a defendant can persuade a jury that he truly was victimized by a government "sting," that federal agents conceived the crime and gave him more than a slight nudge to go along.

Mundy originally wanted to separate the charges and defend the single "sting" count by itself so he could allege government entrapment. Prosecutors took away that option last month when additional, broader charges were filed, alleging a pattern of cocaine use by the mayor.

An alcohol abuse defense could be even trickier. Proving that Barry was an alcoholic during the period when the crimes allegedly were committed would not, in itself, be enough to absolve him from legal responsibility, experts said.

At the most, it would be evidence bearing on whether Barry had the necessary intent to lie to a grand jury when he testified in January 1989 that he did not know Charles Lewis was involved with drugs and that he had neither given drugs to Lewis nor obtained drugs from him.

According to sources, Mundy has decided that the benefits of such a defense are more than outweighed by the disadvantages of showing the mayor's medical records to prosecutors, which he would be required to do under federal court rules if he used the alcohol defense. The mayor and his staff have maintained that Barry was treated earlier this year for alcohol abuse, not for drug abuse, but sources close to the mayor said the records contain evidence that Barry also was treated for drug dependence.

Barry is charged in a 14-count indictment: three felony counts of lying to a grand jury, 10 misdemeanor counts of possession of cocaine and one misdemeanor count of conspiring to possess cocaine. From a defense standpoint, the three perjury counts are the most critical.

Fortunately for the mayor, the three felony perjury charges are based on the testimony of Lewis, whose testimony will likely be challenged as that of a convicted perjurer and drug dealer.

Lewis, who is completing a sentence for his drug and perjury conviction last year, plea bargained with federal prosecutors, promising to testify against Barry in return for a shorter prison sentence.

Lewis was the central figure in the Ramada Inn episode of December 1988, when Barry visited Lewis in his hotel room and D.C. police detectives aborted plans for a drug sting of Lewis after realizing Barry was with him.

The FBI joined the investigation and organized an undercover sting operation against Lewis in St. Thomas, in the U.S. Virgin Islands. Lewis was arrested on March 3, 1989, and was charged with possession and distribution of cocaine.

Lewis was convicted, and later was indicted here on perjury and cocaine charges. He ultimately agreed to plead guilty and cooperate with prosecutors.

Mundy will say the Lewis case shows the lengths to which the government went to obtain a witness who would testify against the mayor. Although that argument could have some jury appeal, some legal experts said, the government's methodology in this investigation is really no different from what it has been in other complicated, multiple-defendant cases.

Mark J. Biros, a former federal prosecutor, said Mundy "is in something of a bind" because a defense based on alleged government overreaching at the Vista Hotel, where Barry was arrested on Jan. 18, would not help defend allegations of prior drug use.

What would be left, Biros said, would be a broadside attack on the government and its tactics in hopes of discrediting the entire case.

"That is a common defense strategy in political corruption and celebrated cases," Biros said. "But it's an open question how that will play. Often, there are jurors who have preconceived notions, and there are others who make up their minds based on something that happens in court -- and it's rarely apparent in advance what that one thing might be."

To bolster that type of defense, Mundy and his partner, Robert W. Mance, would likely highlight for the jury all the witnesses with whom the government has reached agreements on immunity and cooperation. Juries traditionally dislike immunized witnesses, and defense lawyers are expected to explore the reasons that the various individuals decided to cooperate.

In at least one case, that of Georgetown restaurateur Hassan H. Mohammadi, prosecutors agreed that Mohammadi would plead guilty to a misdemeanor although they had evidence he committed more serious offenses.

Lawyers said the defense can try to show that the government charged and immunized Mohammadi and others simply to get Barry.

On the prosecution side, Stephens has filed a motion seeking to prevent Mundy from asserting prosecutorial misconduct during the trial. Judge Jackson has overruled a defense motion to dismiss the indictment on those grounds, but Mundy is expected to use the same theme to attack the government case.

Richard Ben-Veniste, a former Watergate prosecutor, said the question of alleged government misconduct is one for the judge, not the jury, and usually cannot be considered when weighing credibility of witnesses.

Both Biros and Ben-Veniste said Stephens and his assistants should try to treat the Barry case exactly as they would any ordinary drug case. To counter defense attacks with an argument that Barry had a special responsibility as mayor to abide by the law could backfire, they said.

Prosecutors Richard Roberts and Judith Retchin may decide to show deference to Barry in the courtroom, calling him "Mr. Barry" instead of "the defendant."

Mundy also has talked about using a defense based on jury nullification, an obscure but potentially powerful legal strategy in which the defense tries to get a jury to acquit a defendant based on jurors' dissatisfaction with the government -- even if they believe he is guilty.

The ability of the defense to do that could be hampered in two inportant respects. First, jurors are never told they have the power of nullification, and Mundy will be prevented from suggesting it.

Second, the jury questionnaire circulated yesterday among prospective jurors specifically asks whether a juror would be able to reject a suggestion from another juror "that you disregard the law or the evidence and decide the case on other grounds." Prosecutors are expected to challenge each prospective juror who answers yes to that question.