When prosecutors wrapped up their case against D.C. Mayor Marion Barry, they made a point of ending with Doris Crenshaw as their last major government witness.

Prosecutors expected Crenshaw's testimony to be formidable. A former deputy campaign manager in former vice president Walter Mondale's presidential campaign, Crenshaw had told investigators that she had used cocaine with Barry more than a dozen times since 1984, including sometime between Nov. 7 and 10, 1989, during a business trip to the District.

Crenshaw's testimony is the basis for Count 12 of the 14-count indictment, which charges Barry with possession of cocaine "between on or about Nov. 7, 1989 and on or about Nov. 10, 1989." That was the count on which the jury said yesterday it had a verdict -- but it did not disclose it in court.

In her testimony before the jury, Crenshaw was less certain than she had been with investigators about the specific dates of her fall 1989 cocaine use with Barry. But she told the jury she was certain that she had used cocaine with Barry during one of her three or four trips to the District that fall.

Crenshaw told the jury that the cocaine use could have occurred in September, October or November, but that "there is no doubt he visited my room in the fall {of 1989} and used cocaine."

During closing arguments, Barry's attorney, R. Kenneth Mundy, focused on Crenshaw's lack of specificity, and asked the juror to acquit Barry of count 12 because Crenshaw was uncertain about the date.

"If she is as uncertain about that as she was, then it could have happened at another time, another date," Mundy told the jury. Mundy had suggested earlier to the jury that prosecutors were being unfair because a number of the counts charged in the indictment covered a broad period, making it almost impossible to investigate and refute the charges with an alibi.

But prosecutor Judith Retchin told the jury that to find Barry guilty of Count 12, the law only requires the jury to find that the cocaine use occurred "on or about" the dates charged in the indictment.

"Under the law, 'on or about' means if something happened reasonably near the time charged, you can still find the defendant guilty," Retchin told the jurors. " . . . There is no confusion about the fact that November is on or about fall. Miss Crenshaw told you that she was certain it happened in the fall, so that is on or about November."

In his instruction to the jury, U.S. District Court Judge Thomas Penfield Jackson seemed to agree with Retchin: "The proof need not establish with certainty the exact date of an alleged offense," he said. "It is sufficient if the evidence establishes beyond a reasonable doubt that an offense was committed reasonably near the date or period alleged."

Retchin also told the jurors that even if Crenshaw was not exactly certain of the date, there were a number of factors pointing to the time frame charged in the indictment, including a phone log of messages left for Barry. Crenshaw, according to the phone log, left a message for Barry on Nov. 10 at 9 a.m. asking him to "call right away" at the Mayflower Hotel, where she was staying. Crenshaw also testified that hotel records showed that she left the Mayflower on Nov. 10. Crenshaw testified that she remembered using cocaine with Barry in the midmorning as she was packing and getting ready to leave for the airport.

Witness Doris Crenshaw is a former Barry political ally who owns a public finance consulting business in Montgomery, Ala.

Crenshaw was a former deputy campaign manager in former vice president Walter Mondale's presidential campaign. She testified under a limited form of immunity known as "use immunity," which prohibits the government from using her statements against her in any future investigation.

Crenshaw was the 10th witness to testify that she had used drugs with Barry or seen him with drugs.

After her testimony, Crenshaw's attorney, A.J. Cooper, read a statement to reporters saying she "regrets deeply" certain "improper" activities in which she engaged with her old friend Barry. "Ms. Crenshaw believes," the statement said, "that some of us did not make the transition from the '60s we should have, as far as the casual use of drugs is concerned."