D.C. Mayor Marion Barry's drug and perjury trial was abruptly recessed yesterday until Tuesday, when prosecutors expect to call to the stand Bettye Smith, a former Barry girlfriend whom the prosecution has characterized as a reluctant witness.

Unlike previous women who have testified about their relationship with the mayor, Smith has left prosecutors uncertain how cooperative she might be on the witness stand. Sources said she has been balking at publicly implicating Barry.

In court, prosecutors told U.S. District Judge Thomas Penfield Jackson that they did not want to end their case with Smith's testimony. He agreed to a recess until Tuesday.

Meanwhile, Barry lawyer R. Kenneth Mundy told the judge that he will be ready to start his side of the case by the middle of next week, and that he plans to call 10 to 15 witnesses. It was the first foreshadowing he has given of his defense plans.

Mundy said no decision has been made on whether Barry will take the stand. There could be risks either way, criminal lawyers said.

Mundy said of the upcoming defense case: "It's going to be full of thrills and surprises."

According to sources, Smith has told authorities that she provided drugs to Barry on several occasions and that she used cocaine with the mayor in January, shortly before the Vista Hotel sting.

One source familiar with the mayor said that Smith has continued to socialize with Barry even after her decision to cooperate with authorities, and that the two have spent time together since May 10, when Barry was hit with a second indictment, which enlarged the case against him. Of the new charges contained in the May 10 indictment, one count, alleging cocaine possession between New Year's Day 1990 and the Jan. 18 sting, was based on grand jury testimony by Smith.

Smith also can corroborate the testimony of several witnesses who had said she was present at some key locations where Barry used cocaine, sources said. One close Barry friend, A. Jeffrey Mitchell, testified this week that he told a grand jury that he believed Smith had supplied cocaine to Barry.

Smith's appearance at the trial has been in doubt since last week, when prosecutors obtained an order from Jackson compelling her to testify. On Thursday, Jackson issued a warrant for Smith's arrest after her lawyers told the judge at a bench conference that Smith would refuse to testify until after Monday, when her father is scheduled to undergo cancer surgery in Tennessee, according to a source familiar with the case.

Jackson has placed the transcript of the bench conference under seal, but a source said Smith checked herself into a hospital in Chattanooga for stress.

One source said Barry and Smith have met socially on several occasions in the past months. Another source who has spoken to Smith recently said Smith is "very worried about testifying." According to a log of telephone calls made to Barry's command center on weekends and after business hours, Smith called Barry at least 70 times from June 13, 1986, to Jan. 14, 1990.

Another source said Smith agreed to cooperate only after law enforcement officials made it clear that they would "go after her" on drug-related criminal charges if she did not aid in the investigation.

Although Smith's reluctance is the most pronounced, other prosecution witnesses friendly to Barry have seemed to be sad or ambivalent on the witness stand. Lloyd N. Moore Jr., Theresa Southerland, Darrell Sabbs and Mitchell, in varying degrees, signaled only limited willingness to implicate their friend.

Barry left the courthouse shortly after noon yesterday after it was clear there would be no more testimony until Tuesday.

The mayor stopped to tell reporters that he was happy that his friend and former human services director, David E. Rivers, was acquitted of bribery charges Thursday. "This Justice Department in this case has ruined reputations, has caused over two or three dozen minority businesses to go out of business. And well the people spoke," Barry said.

Assistant U.S. Attorney Richard W. Roberts said in court that the government will not seek to introduce scientific testimony about hair samples taken from Barry on the night of his arrest in January. Roberts said the government decided not to present the evidence because it did not want to risk having a conviction overturned by an appeals court that could decide the evidence was admitted improperly.

According to pretrial motions, the samples would have showed that Barry used cocaine in the weeks before the Vista arrest. The defense, however, was prepared to present expert testimony questioning the validity of hair analysis.

Roberts said that, in addition to Smith, the government plans to call two more witnesses: Montgomery, Ala., businesswoman Doris Crenshaw, and D.C. police Detective James Pawlik. Crenshaw, an old civil-rights ally of Barry's, is expected to testify about several instances in which she used cocaine with Barry.

Roberts said Pawlik would present a summary of an analysis of the mayor's cellular telephone bills.

Jackson told jurors that they would have a three-day weekend because the prosecution's next witness, "by reason of personal problems, is unable to appear until Tuesday morning." As Jackson spoke, several of the jurors appeared to laugh, then held their heads in their hands. The 12 jurors and six alternates have been lodged in an area hotel and kept away from most outside contacts since June 18.

Earlier in the day, Mundy struck several recurrent themes during cross-examination of Sabbs, who testified that he and Barry used cocaine together about five times. Sabbs, 40, appeared to be a willing foil in Mundy's efforts to raise questions about FBI tactics and Sabbs's recollection of specific dates.

Mundy repeatedly has suggested that an overzealous FBI singled Barry out while overlooking more serious crimes by others.

Sabbs agreed with Mundy on cross-examination that prosecutors did not appear to be interested in finding out much about who supplied Sabbs with the drugs he shared with Barry during an August 1989 incident at the Ramada Renaissance hotel downtown. The alleged drug use was the basis for one of the possession counts against Barry.

Sabbs, who nodded and smiled at Barry when he entered the courtroom, told Mundy that he felt the FBI had applied "intense" pressure on him. He also said that he sometimes changed the dates of events -- sometimes by years -- after the FBI presented him with evidence indicating his original recollection was not correct.

But Sabbs said he had no doubt that he had used cocaine with Barry.

Staff researcher Matthew Lee contributed to this report.