Jesse L. Jackson urged D.C. Mayor Marion Barry yesterday to announce he will not seek a fourth term, saying such a public declaration could serve as powerful leverage in plea negotiations with U.S. Attorney Jay B. Stephens.

As jury selection in Barry's perjury and drug trial entered its third day in U.S. District Court, Jackson said in an interview that the mayor seemed willing to "take a step off dead center" and announce that he would abandon all plans for reelection.

"His candid declaration of his plans would be a major step toward further creating a climate for a settlement," Jackson said. "Declaring he won't run is stronger leverage. If he agrees not to be a part of the equation, then the question really is: Why then prosecution and persecution?"

Sources familiar with Barry's current thinking said late last night that the mayor is not prepared to make that declaration now. "We are far from that," said one source.

Meanwhile, officials in the White House, the Justice Department and the national Republican Party said yesterday they were unaware of any preliminary contacts by Jackson or Del. Walter E. Fauntroy (D-D.C.) that some Democratic sources said were initiated earlier in the week.

"We have checked with everybody we can find who might have any relevance to this matter and . . . there is no basis for that story," said White House Press Secretary Marlin Fitzwater. "We have no involvement in the case -- no contact."

Although Stephens has said that he is not interested in obtaining Barry's removal from office -- a resignation is "irrelevant" to the case, he said last week -- an announcement by Barry that he would forgo a fourth term might give the mayor a bargaining chip in plea negotiations. Stephens has not publicly addressed the issue of a promise by Barry not to seek reelection.

Barry has privately told close associates that he does not want to plead guilty to a felony charge, which probably would entail a prison sentence, and has expressed confidence about starting a career outside politics if he is not mayor next year.

Jackson's comments, which followed several recent conversations with Barry and at least one discussion with R. Kenneth Mundy, the mayor's attorney, contrasted sharply with the civil rights leader's behind-the-scenes role in the mayor's camp before the start of the trial this week.

Since the mayor's Jan. 18 arrest, Jackson said he has conferred with Barry on a "private level of sharing and counseling," rarely speaking out on the mayor's case "because I felt it should be tried in the courtroom and not in the newsroom and in the streets."

However, with the apparent blessing of Barry and Mundy, Jackson in recent days has taken the somewhat unusual step of commenting directly on the trial and possible plea negotiations. Mundy said yesterday the two sides are not talking and that "there's no offer, either way." He made no objection to Jackson's involvement, although he noted, "We don't seek it and haven't particularly asked for it."

In a move similar to Jackson's, Fauntroy, a mayoral candidate, also has called on Barry and Stephens to reach a plea agreement and reportedly has contacted some of his Republican colleagues in Congress to help create a framework for possible negotiations. However, Republican leaders on Capitol Hill said yesterday they were not aware of such efforts by Fauntroy.

Jackson said in the interview that he had discussed the Barry case with neither Stephens nor U.S. Attorney General Dick Thornburgh, with whom Jackson became friendly when Thornburgh was governor of Pennsylvania.

Although Jackson said it would be "injudicious" to discuss the case with Thornburgh, his remarks in a series of media interviews yesterday seemed intended for the ears of the attorney general and Stephens.

While questioning some of the actions of the FBI and other federal authorities in the sting that resulted in Barry's arrest, Jackson also said his remarks were not intended as an attack on Stephens.

"I'm not attacking his integrity, I'm appealing to his judgment," Jackson said.

"This situation has soiled hands in all directions," Jackson said.

Jackson said a fair compromise would include Barry pledging not to run in exchange for Stephens's allowing the mayor to plead to a lesser charge than a felony -- a move that sources said the prosecutor is unwilling to do at this point.

"If those two things happen, you could spare a lot of pain in the city," Jackson said of his proposed compromise. "After all, not only is Marion Barry about to go to trial, so is the Justice Department . . . . It's bigger than Jay Stephens and it's bigger than Marion Barry."

Barry is standing trial on 14 criminal counts, including three felony charges of lying under oath to a federal grand jury and misdemeanor charges of cocaine possession.

Meanwhile yesterday, a small group of Barry supporters continued a vigil outside the courthouse, where jury selection proceeded so slowly that a few spectators dozed.

Mundy announced at a noon news conference that he had removed Anita R. Bonds, the mayor's top political adviser, from his list of prospective witnesses. Bonds spent all day Tuesday seated at the defense table next to Barry, a violation of normal procedure barring prospective witnesses from the courtroom.

Staff writers Ann Devroy, John E. Yang and Sharon LaFraniere contributed to this report.