The trial of D.C. Mayor Marion Barry is set to begin in earnest today, after selection yesterday of a jury and alternates. Charles Lewis, Barry's old friend and now his chief accuser, is expected to be the first prosecution witness.

Opening statements, the first broad brush strokes by prosecution and defense, will follow welcoming instructions from U.S. District Judge Thomas Penfield Jackson at 10 a.m. With jury selection completed, all the players had taken their places in the mayor's drug and perjury trial. Lewis is expected to take the lead-off position on the witness stand by afternoon.

Barry faces 10 counts of misdemeanor cocaine possession, one count of misdemeanor conspiracy to possess cocaine and three felony counts of lying under oath to a federal grand jury. Lewis is a central figure in several of the possession counts -- including the charge that Barry smoked crack at a downtown Ramada Inn in December 1988 -- and in all three allegations of perjury.

"All right, we have a jury," Jackson declared at 10:29 a.m. yesterday, 36 minutes after a marshal's double knock announced his arrival on the bench. Few words were spoken in the hushed, expectant courtroom besides the names and numbers of panelists: once as they filed to the jury box, again if they were struck by either side.

The 18 District residents who will sit in judgment of their mayor are a varied lot. Fifteen women and three men were left in the box when the two sides ran out of peremptory challenges. There are 13 blacks and five whites. Jackson impaneled them as 12 jurors and six alternates, then placed them in the custody of deputy U.S. marshal Albert Crews for sequestration. Marshals escorted the jurors to their homes to pick up clothing and other belongings, then brought them to an undisclosed hotel, where they will live for the duration of the trial.

In a speech after the jury selection to about 500 city workers, Barry said he will place his fate "in the hands of Judge Jackson, 12 jurors and God -- and let go."

Only the judge and the lawyers know which of the 18 jurors are alternates. Most judges keep that information from the panelists to encourage all of them to pay attention to the evidence.

Race, an emotional undercurrent of the trial, was conspicuous in yesterday's selections. Fifteen whites and 22 blacks were called to the jury box. The mayor's lawyers used 10 of their 12 strikes against whites. Prosecutors used all seven strikes against blacks.

Barry, whose 12-year dominance of local politics bespoke a shrewd sense of his electorate, repeatedly leaned over the defense table for whispered conferences with Anita Bonds, manager of his recently abandoned reelection campaign, and lawyers R. Kenneth Mundy and Robert W. Mance.

Minutes sometimes passed between strikes yesterday as the mayor and his advisers weighed the tactical significance of every choice. Barry would lean and point at a questionnaire, tilt back his reading glasses to gaze deeply toward the box, then lean down again to speak in Mundy's ear. Some prospective jurors smoothed their clothing and shifted in their seats. Others stared over the lawyers' heads, conveying a studied indifference to their fate.

Except under strict supervision, Jackson ordered, the marshals "shall suffer no non-juror to converse with or have contact with any member of the jury." All accounts of the case will be cut out of newspapers and magazines before delivery to the panel, and their radios and television sets will be closely controlled. In return, the government will feed the jurors three meals a day (up to "two cocktails at the dinner meal") and "some type of modest refreshments" in the evening.

The mayor's first two strikes from the panel were black men who appeared to be in their thirties. Dwayne Forrest, the brother of a corrections officer, apparently sealed his dismissal with the following declaration on the witness stand June 8: "He is the mayor of the District of Columbia. That doesn't give him the right to go out and smoke crack or whatever he did, and I feel he should be punished if that's the case."

Second to be excused on a Barry strike was Michael Hunter, who called the mayor "egotistical" and "pompous" from the witness stand last Wednesday, and expressed the view that Barry had lied in his election campaigns. "My opinion of him as a politician is not favorable," Hunter said.

All 10 of the mayor's remaining strikes were used against whites. The six women and four men included a history professor, a scientist and a copywriter in promotions at The Washington Post. Most had arrived for jury service with doubts about the mayor. All had pledged to set those doubts aside and decide the case on the evidence.

Alternating with the mayor's strikes were strikes by the prosecution. Assistant U.S. Attorneys Richard W. Roberts and Judith E. Retchin, who had been allocated five fewer strikes than the defense, skipped several turns in the middle to prevent the mayor from reshaping the jury with five unanswered strikes at the end.

Among the strikes by the prosecution were Sarah Rhodes, who testified that she kept the mayor in her prayers; Kenneth Gaines, who disapproved of undercover operations against "small-time" drug offenders; Walter Oliver, who said "the FBI set him up" at the Vista Hotel; Mark Dixon, who smiled broadly at the mayor through his first several questions on the witness stand; and Yvonne Francis, who testified that "people should be given a second chance if they make mistakes" and said the mayor had been targeted "because of his color."

When he emerged from the courthouse, Barry shook hands with Mundy and joked with reporters before entering his car. "The canaries are coming," Barry said, an apparent reference to the array of expected prosecution witnesses prepared to testify against the mayor.

Afterward, Barry made a brief appearance at an awards ceremony for workers in the D.C. Department of Employment Services.

In an obvious reference to the crowd of former friends and associates expected to testify against him, Barry added: "I've changed some of my friends around, I'll tell you that . . . . My grandmother taught me, whenever you make a friend, remember that person may be a potential enemy. So be careful."

During the trial, expected to last at least a month, day-to-day operations of the District government will be the responsibility of City Administrator Carol B. Thompson, according to city officials.

In a recent interview, Thompson said Barry had not withdrawn the mayoral powers he granted to her in January before he left Washington for seven weeks of addiction treatment.

But, she added, referring to the trial, "Clearly, it's a difficult time on everybody."

Staff writers R.H. Melton and Michael York contributed to this report.