The special Alexandria grand jury impaneled last month to probe allegations that Director of Public Safety Charles T. Strobel prematurely halted a 1984 drug investigation has heard evidence from more than a score of witnesses, some of whom have testified on matters that appear unrelated to the drug probe.

Fairfax County Commonwealth's Attorney Robert F. Horan, who is special counsel to the grand jury, said yesterday that "as far as I know, the investigation has not been expanded." Horan goes before the grand jury during questioning of witnesses and is not present during the jurors' deliberations.

Now in its third week of hearing testimony, the 11-member panel has heard from at least 25 witnesses, some of whom have said they have been questioned on the drug probe, on allegations of criminal activity by a high-ranking police officer and on how Strobel handled those allegations. Some witnesses said they were asked about friendships and sexual preferences of some policemen.

One witness said he told the special grand jury in response to questioning that he was ordered by Strobel to stop investigating information he had received linking two policemen from another jurisdiction to a 1971 murder in Arlington. There is no apparent indication that that incident was related to the drug probe.

Strobel's attorney, David Fiske, declined to comment on those allegations. Strobel is set to make his second appearance before the grand jury next Tuesday, Fiske said.

Some witnesses said they were initially questioned by Horan and then by members of the panel. The special grand jury has the power to review allegations and make a report and recommendations, but not to indict. Indictments could be sought from a regular grand jury on the basis of the report.

The witnesses have included Strobel and several police officers as well as former members of the force, the police informant who worked on the drug case, City Manager Douglas Harman and former vice mayor James Moran. Alexandria Sheriff Michael E. Norris, who a former Alexandria police detective alleged was a focus of the drug investigation, also testified.

Moran, who testified for more than two hours Monday, said yesterday the grand jury asked if he had heard allegations of a criminal nature, apparently unrelated to the drug investigation, against a high-ranking police officer and asked what he had done about them.

Moran said he had heard the allegations and had checked into them with Strobel, Harman and city Commonwealth's Attorney John E. Kloch. Moran said Strobel told him that no crime had been committed.

Moran said he was asked about other incidents by the grand jury but declined to say what they were.

Harman said his appearance before the special grand jury was "uneventful." He said he was asked about the administrative structure of his office in relation to the police department and about what he knew of the 1984 drug investigation.

Harman would not discuss details of his grand jury testimony, but told a reporter he knew of a drug investigation "involving some restaurant" in the city but "as far as I can remember, there never was a situation where I was being consulted about an investigation into a particular person."

Harman said the first he learned of any connection between the investigation and Norris was when he was told Norris "became someone to look at" because he frequented the restaurant. But at the same time he was told Norris "hadn't done anything" wrong.