Defense lawyer R. Kenneth Mundy completed his cross-examination yesterday of D.C. Mayor Marion Barry's key accuser, questioning convicted drug dealer Charles Lewis's credibility but leaving virtually unchallenged Lewis's allegations that he and Barry smoked crack together many times.

At one point yesterday morning, U.S. District Judge Thomas Penfield Jackson lost patience with Mundy's line of questioning and said at a bench conference that the cross-examination had gone nowhere.

"You haven't touched on a substantive issue yet with respect to this testimony," said Jackson, according to a transcript.

Mundy responded: "The jury will be the judges of the effect of the testimony."

"What you have touched upon is his credibility, and you have effectively placed his credibility into question," Jackson shot back. "But you haven't dealt with the substantive issues in the case."

Lewis, a former employee of the District and Virgin Islands governments, testified this week that he smoked crack with Barry at a Washington Ramada Inn in December 1988 and in the Virgin Islands in 1986 and 1988.

"I don't think Charles Lewis helped {the prosecutors} to the extent of proving {a crime} beyond a reasonable doubt . . . . I think he got a sweet deal," Mundy told reporters outside the courthouse, referring to Lewis's plea agreement with the government. Asked about his cross-examination, Mundy said, "It wasn't up to what I wanted it to be."

Lewis is the prosecution's key witness to support the most serious charges against Barry: that the mayor lied to a federal grand jury in January 1989 when he testified he did not know Lewis was involved in drugs and that he had not given or received drugs from Lewis.

Barry also is charged with 10 counts of cocaine possession and one count of conspiracy to possess cocaine. The perjury charges are felonies and carry mandatory prison sentences; the remaining charges are misdemeanors, for which first-time offenders can be placed on probation.

Lewis is one of the 19 alleged co-conspirators who prosecutors claim joined with Barry in possessing cocaine.

In yesterday's questioning, Mundy tried to show that from 1985 to 1987 Lewis was involved in his own cocaine-dealing conspiracy, and that it had nothing to do with the mayor.

Lewis testified that he came up with "a partnership scheme" to distribute cocaine with D.C. employee James McWilliams and three other people, but that the plan never got off the ground. That unsuccessful drug plan came after a series of successful cocaine deals in which Lewis took part between 1985 and 1987, according to Lewis's testimony. He said he had acted as a courier, bringing cocaine to the District from Florida, and that one of those involved was McWilliams. Lewis testified, however, that McWilliams did not use the drugs. Rather, Lewis said, McWilliams gave the cocaine to a close friend, Yvette Parron, a former hearing officer for the D.C. traffic adjudication office.

McWilliams has pleaded guilty to aiding and abetting the possession of cocaine by Lewis. McWilliams agreed to plead guilty in an agreement with prosecutors, who also have promised immunity to his friend Parron, sources said.

McWilliams is expected to testify today, but Assistant U.S. Attorney Judith E. Retchin already was trying to shore up McWilliams's credibility against the expected onslaught by Mundy, who has characterized him as a drug dealer in league with Lewis.

Retchin asked Lewis in several ways whether McWilliams had used or sold cocaine, and each time Lewis answered that McWilliams had not.

After his testimony, Lewis and his lawyer talked to reporters outside the courthouse. Declining to talk about the case, Lewis said only that he was "feeling good" and happy to have finished his role in the trial.

Retchin also had trouble with Jackson, who has coached her each day in open court on the proper way to conduct her questioning. Yesterday, Jackson, a former trial lawyer, stepped in, as he has previously, to suggest how Retchin might phrase a question.

The issue was whether Lewis had heard rumors about Barry's alleged drug use in 1986, when Lewis testified that he first smoked crack with the mayor. After trying to elicit that response but failing with a wordy, confused question, Jackson took over.

Looking down at Retchin, the judge said, "'Did you have a reason to believe?' Try that."

Later, Retchin once again had difficulty as she tried to compare McWilliams's alleged drug involvement to the mayor's, trying to show that McWilliams had not sought to make a profit.

When Mundy objected to the question and Jackson sustained him, Retchin hestitated. Then, she asked the judge, "Is it form {of the question} your honor?"

"It's a lot of things," Jackson said. "If you want to press it, come to the bench."

At the bench, Jackson said he understood Retchin's idea, but he said her wording was wrong. He added, "But I don't think I should suggest to you how you want to say it. Find some other way to formulate it."

After another series of questions that prompted a successful objection by Mundy, Jackson finally took over, asking Lewis, "Did Mr. Barry do anything different with the cocaine than Mr. McWilliams did, as far as you know, in terms of transferring possession of it to a friend?"

After Lewis said "no," Jackson asked Retchin, "Is that the point you were trying to make?"

"Yes, your honor," Retchin said.

Another witness, Ramada Inn employee Orlando Berrios, testified that he was on duty two days in December 1988 when Barry visited Lewis at the hotel, but he was unable to corroborate Lewis's allegations that Barry used drugs there.

Berrios played straight man for one of the trial's lighter moments so far. Asked if he could identify Barry in the courtroom, he said, "Of course," and sort of smiled and waved at the mayor.

Jackson broke into a broad grin, saying the record would reflect the in-court identification, while Barry flashed his trademark smile and waved back to Berrios. Before it was over, most of the jurors were smiling, too. Staff writers Barton Gellman, Tracy Thompson and Elsa Walsh and researcher Matthew Lee contributed to this report.