An Alexandria Circuit Court jury acquitted a former condominium project manager yesterday of charges that he bugged an Alexandria condominium owners' meeting after the judge instructed them that the secret recording was not illegal under Virginia law unless the manager heard or tried to hear it.

Judge Donald Haddock instructed the jury at the end of testimony in the two-day trial that the "interception . . . of an oral communication" is a felony in Virginia, but interception is defined in the law as the "aural acquisition" -- or hearing -- of what is recorded.

David Ralph Thompson, former manager of the project, was charged with illegal "interception" of the meeting, in which the condo owners and their attorney were discussing their lawsuit against the project developer.

Haddock told jury members that even if they believed Thompson placed the microphone behind a ceiling vent, where it was found by the owners, and set up the tape recorder to which the microphone was connected, they could find Thompson not guilty if they doubted he "ever heard or endeavored to hear the conversation recorded . . . ."

Thompson was arrested in June after owners of 27 apartments in the Sentinal of Landmark condominium project in the west end of Alexandria discovered the concealed microphone during a meeting in the building's community room. The meeting was held to discuss a suit in which they charged the condominium's developer, John F. DeLuca, his attorneys and real estate agents with fraud and violations of the Virginia Condominium Act.

Thompson, a former employe of DeLuca, was manager of the building during the time the developer owned it.

Gary A. Gustafson, one of the owners at the meeting, testified that he found the microphone and helped trace the wire connected to it through the ceiling and down the hall to an electrical equipment room, where they found a tape recorder.

Alexandria police investigators and a fingerprint expert testified they found Thompson's fingerprints on the recorder, but not on the microphone or the earphones that were found attached to the recorder. Thompson rented the microphone from a Fairfax County sound equipment company on June 1, two days before the condo owners' meeting, according to the testimony of Meridith Hackett, the equipment company's office manager. She said he had returned to pay for the microphone on June 5, saying he had lost it.

Albert J. Ahern Jr., Thompson's attorney, said Thompson's fingerprints were not found on the mircrophone or earphones, and that there was "no evidence he heard or tried to hear the recording."

Prosecutor Randy Sengel argued that "the tape starts when the meeting starts . . . . This means the defendant . . . was sitting there listening to what was going on in the meeting room so he could flip the switch and record" the meeting when it began.

Mark B. Mitchell, one of the owners at the meeting, said he saw Thompson in the hallway outside the meeting room about an hour before the meeting began, and saw him again after the recording equipment was found.

The trial of the condo owners' suit ended a month ago, but Circuit Court Judge Donald H. Kent has not yet issued a ruling.