A flamboyant Northern Virginia private detective installed an illegal wiretapping device on the telephone of an undercover policewoman who had posed as a suspicious wife seeking evidence her husband was secretly calling another woman, a D.C. police detective told a Northern Virginia court yesterday.

Det. Michael E. Hubbard testified in Arlington Circuit Court that Joel L. Kaplan, a 31-year-old private investigator and head of Action Investgative Services of Alexandria, agreed to install the illegal surveillance equipment for a cash payment of $3,000.

Kaplan, a black belt karate expert who specializes in child custody and divorce cases, is charged with possession of illegal wiretap equipment and attempted illegal wiretapping. He has pleaded innocent of the charges, each of which carries a maximum sentence of five years in prison.

Hubbard also testified that the private investigator boasted to him of having performed more than 7,000 wiretaps in the past 14 years. Tapes played in the court yesterday also had a man proscutors said was Kaplan telling hubbard that he possessed sophisticated electronic equipment valued at $175,000, as well as a specially outfitted $25,000 van that contained electronic gear.

Under Virginia law placing recording devices on telephones is illegal without the consent of the telephone subscriber unless authorized by a court order and performed by police officers.

During yesterday's hearing -- one of the first cases of its kind in the Virginia suburbs -- Hubbard testified that he met Kaplan during an undercover assignment last winter at an electronics seminar held at the Watergate Hotel. Hubbard said he was posing as "Mike Lewis," a D.C. private eye at the time, and said Kaplan told Hubbard to call him if he ever needed eavesdropping equipment.

Hubbard said he did precisely that on April 15 when, he called Kaplan for help in a divorce case. Hubbard said he told Kaplan that his client, a young Arlington woman, was seeking proof through telephone wiretaps, of the infidelity of her husband. Prosecutors introduced tape recordings of the conservations between Hubbard and a man they said was Kaplan, discussing the illegal wiretap.

"She's convinced that the minute she leaves town (on a brief vacation) her old man's going to pick up the phone and call the main squeeze," Hubbard said to the man, using the lingo of private investigators to describe the fictitious girlfriend. In another conversation, Hubbard told Kaplan, that the woman, who was an undercover officer, was "game for the bread and she'll pay up front."

According to Hubbard, Kaplan agreed to install the wiretaps using his own equipment. "He indicated that the equipment he had was far superior to any federal agency with the possible exception of the DEA (Drug Enforcement Administration)," Hubbard said.

After Kaplan agreed to take the case, Hubbard testified, the Alexandria investigator told him to rent a car and meet him for breakfast at an Arlington restaurant the following day. After the breakfast meeting, the two men drove to a nearby garden apartment in the Buckingham section of North Arlington where the undercover policewoman was waiting.

Kaplan entered the apartment carrying a briefcase full of electronic equipment, according to Hubbard, and proceeded to install the bugging device on the woman's telephone. Arlington police Officer Rebecca Hackney, who was posing as a suspicious wife, said that she and Hubbard watched Kaplan install the device.

Hackney testified that Kaplan told her "this is the third time I've done this." When she looked quizzically at him, Hackney testified Kaplan said laughing, "The third time this week."

Hubbard said that Kaplan then installed a receiving device in the trunk of the rental car which was parked outside the apartment. The plan, according to Hubbard, was that he would make daily checks of the device installed in the rental car, which should have record all conversations on the tapped telephone.

Kaplan's attorney David Sher disputed prosecution claims that Kaplan had performed illegal wiretaps. Sher argued that no crime had occurred because the equipment Kaplan possessed was legal and because Kaplan did not listen to any tapes.

"He merely acted as an electronics consultant and hooked [the device] up," Sher said. "The police department never had any intention to allow interception [of telephone calls]. Mr. Kaplan never intended to listen to those tapes." The trail is scheduled to continue today.