A street-level cocaine dealer has told law enforcement investigators that she sold cocaine to D.C. Mayor Marion Barry on a regular basis and that Barry at times had a running tab of hundreds of dollars in cocaine debts, sometimes more than $1,000, sources said.

Lydia Pearson, who is expected to testify today and has been described by prosecutors as a cocaine addict, has told law enforcement investigators that in 1988 and 1989, she regularly supplied cocaine to Barry, often weekly, and that Barry frequently called her to set up cocaine purchases, according to sources.

Pearson's telephone number appears regularly on a log of phone calls made by Barry that is expected to be introduced into evidence by prosecutors, according to sources. It appears once on a log of callers to the mayor's command center.

Pearson told investigators that when she began dealing directly with Barry, he would regularly buy crack cocaine -- up to $100 worth at a time, according to sources. Pearson told investigators that Barry would go to her house to pick up the drugs or she would deliver the cocaine to him, sometimes at his office.

Law enforcement officials consider Pearson central to proving the charge of conspiracy to possess drugs because her testimony is expected to bolster the argument that Barry was a heavy drug user. Testimony that Barry would risk buying cocaine from a street dealer could be an indication that he used drugs regularly, a key element of the conspiracy charge, a source said.

The other witnesses who have testified or are expected to testify that they supplied drugs to Barry were professional people with city contracts or close friends.

Hazel Diane "Rasheeda" Moore, a former girlfriend of Barry's, testified that she and Barry had set up a "credit" arrangement with Pearson and Pearson's friend, Ron Manning, to buy cocaine because she and Barry were "buying cocaine from {Pearson} and her friend Ron so often that . . . the mayor and I set up a credit with them."

"I would go to Lydia's house . . . and get the cocaine, and on the belief that I would be paying her the following day or either that evening once I had been with the mayor," Moore told the jury.

Moore also testified that she and Barry once used cocaine at Pearson's house because she and Barry were pressed for time. "I suggested that we go to Lydia's house since we were going to purchase the cocaine from her and the time was of essence because he had somewhere to go after our meeting," she testified.

But Moore, whose mother lived across the street from Pearson, told the jury that some time after she and Barry began the credit arrangement with Pearson and Manning, Barry instructed the couple not to allow Moore to buy cocaine on credit unless they first received Barry's permission. Moore said Barry took this action because "I began to get cocaine on credit without the mayor knowing it." At that point, Moore testified, she arranged for Barry "to pick the cocaine up from {Pearson} on his own."

Prosecutor Richard W. Roberts described Pearson in his opening statement to the jury as a cocaine addict who "has tried to break free from that habit without success." He also said that Pearson would testify that in September 1988 she delivered crack cocaine to Barry in the executive offices of the Frank D. Reeves Municipal Center.

Roberts said she will testify she "handed {Barry} crack cocaine with one hand and her job application with the other."