A Fairfax County judge yesterday disapproved the Alexandria police department's use of a male civilian volunteer to gather evidence in the city's crackdown on massage parlors, saying both the undercover agent and the masseuse were equally guilty of violating the city's ban on massages by members of the opposite sex.

In dismissing four charges against Deborah Candy Stroud, 26, Fairfax County District Court Judge F. Bruce Bach said, "I don't think I can possibly with good conscience find this girl guilty of doing acts that the police initiated - in effect, did - the same acts (I don't know), who's the bigger whore in this case."

Yesterday's ruling in Alexandria General District Court cast doubt on whether the city attorney's office can successfully prosecute subsequent cases against masseuses based on evidence obtained by the civilian, 24-year-old Michael Kevin Brennan.

Brennan, a bearded security guard, testified yesterday that on the night of July 13, he went to the New Towers Massage Parlor, 1813 Duke St., to obtain "services." He said that Stroud quoted the prices and Brennan said he paid $40 for 40 minutes.

"She led me down the hallway . . . I gave her $40 in cash. She told me to get ready and left the room," Brennan said. He said he removed his clothes, and when the defendant returned, "She told me to take her clothes off."

Brennan said he lay down on his stomach, and the defendant "knelt beside me on the bed."

"She said she couldn't put her hands on me. I pushed them (her hands) down on my shoulder," Brennan testified and then much of the rest of his body, including his genitals. Brennan also testified that he asked for extra services, but was denied.

Brennan said he had been enlisted by the Alexandria police department in April, "to get what I could get and testify later."

Defense attorney Frederick W. Ford called the use of civilian investigators "a conspiracy" on the part of the Alexandria police and argued that Brennan "broke the very law he is charging the defendant with."

Police Chief Charles T. Strobel testified in court yesterday that although he supported the use of civilians, he did not sanction any "soliciting," on their part.

Deputy Chief Clyde Scott testified that he initiated the use of civilian volunteers on the recommendation of then Commonwealth Attorney William L. Cowhig. "We wanted to see what we could come up with," Scott told the court, "any illicit activity . . . prostitution, cross-sex messages."