A former Alexandria police officer, testifying yesterday in the federal perjury trial of city Police Chief Charles T. Strobel, said he gave Strobel information of misconduct by three officers but that Strobel took no action on the matter.

Louis Pugh said that in 1974 he played a tape recording for Strobel on which a prostitute spoke of having sexual relations with three policemen. He said under cross-examination, however, that he had made some errors in his testimony before the federal grand jury that indicted Strobel. He also said he had lost the original tape recording.

The government is seeking to prove that Strobel lied to a grand jury when asked how he handled reports of sexual misconduct by an Alexandria policeman and two Fairfax County vice officers. Strobel, who is on paid administrative leave, is charged with six counts of perjury and six counts of obstruction of justice. He has denied the charges.

"This case is based on false testimony given to a grand jury," Strobel's attorney, Plato Cacheris, said in his opening remarks on the first day of Strobel's trial in U.S. District Court in Alexandria.

Acting U.S. Attorney Justin Williams told the trial jury yesterday that Strobel repeatedly told the grand jury that he did not recall hearing the allegations. But, Williams said, Strobel "did remember them when he testified before the grand jury."

Williams said he will present evidence, including internal memos, showing that Strobel recalled the allegations and that one of them had "stayed and preyed on his mind" before Strobel's appearance before the grand jury last fall. The prosecutor said that on six occasions Strobel took no action when reports of misconduct were presented to him.

Pugh testified that he recorded a conversation with a prostitute identified as Sharon Swim in October 1974 in which she said she had "more sexual contacts" with a city vice officer and "admitted having sexual relations with two Fairfax County police officers in the past."

After Pugh played the tape for Strobel, the chief said that "the best thing to do was for me to be quiet about the tape," Pugh testified. He added that after making copies of the tape in 1978 for two other Alexandria investigators, he lost the original.

U.S. District Judge Richard L. Williams permitted a copy of the tape to be played for jurors, but it could not be clearly heard by spectators.

Under cross-examination, Pugh said he "was mistaken on the time frame" when he told the grand jury last year he had recorded the conversation in April 1974.

Pugh also testified before the grand jury that he had taken a woman into Strobel's office "and she sat there and told him" that an Alexandria police officer had attempted to rape her. Yesterday, Pugh said that this testimony "was not accurate" because he did not know whether the woman had ever talked to Strobel about it.

Pugh said he also told the grand jury that Swim told him she had been "falsely arrested" in Alexandria by two Fairfax County vice officers.

But according to Fairfax police records presented in court, Swim was arrested for prostitution in Fairfax County.