A flamboyant private investigator who allegedly preformed illegaleavesdropping for an undercover police officier posing as a suspicious wife was indicted yesterday by an Arlington grand jury on wiretapping charges.

Joel K. Kaplan, a black belt karate expert and head of Action Investigative Services of Alexandria, allegedly agreed to install eavesdropping equipment to monitor the calls of the errant husband, but said it was illegal and would cost $3,000, according to affidavits filed in the case.

Kaplan, 31, also allegedly told the undercover officier he had preformed more than 7,000 wiretaps using equipment more sophisticated than that of any police force in the Washington area, according to the court papers.

The three-count felony indictment grew out of a month-long investigation by Virginia state police and officers from the District of Columbia, Alexandria, and Arlington and Fairfax counties.

According to court documents, District Det. Michael E. Hubbard, an undercover officer posing as a private investigator, was introduced to Kaplan at an electronics seminar in Washington.

Kaplain alledgedly told Hubbard that he had electronic equipment worth $200,000 that could record up to six and a half hours of conversation from as much as a half-mile away from the source of a wiretap, the affidavits said.

Last Tuesday, Hubbard, still in his role as a private investigator, told Kaplan he needed help with a case and introduced Kaplan to the female undercover agent for whom Kaplan allegedly performed the illegal surveillance, according to the documents.

Equipment that included a 1979 Ford van, an array of sophisticated electronic surveillance gear, a diagram of a housing development and a portable toilet was seized by Fairfax County detectives in a search of Kaplan's home in the Hollin Glen section of the county last week, court papers said.

Reached at his office, located behind a beauty parlor near the Shirley Duke Apartments on Duke Street in Alexandria, Kaplan yesterday denied the allegations in the indictment. "That's not even close," said Kaplan, adding there are "absolutely no grounds for prosecution."

Under Virginia law, wiretapping is illegal without consent of the telephone subscriber, except when authorized by the state police or federal authorities.

Kaplan's indictment followed his arrest last week in Arlington on charges that he used information collected through an illegal wiretap.

Robert Martin, the state police officer in charge of the Culpepper office, said Kaplan was arrested shortly after noon on April 16 at the Sears parking lot on Duke street. Kaplan was driving a 1969 gray Mercedes at the time of his arrest by a team of 15 officiers, authorities said.

Arlington prosecutor Henry E. Hudson said yesterday that an investigation conducted after the arrest of Kaplan, who is free on personal recognizance, produced enough evidence to present the cases to the grand jury.

If convicted, Kaplan who specializes in divorce and child custody cases and employs 22 part-time guards, faces a maximum prison term of five years on each of the four charges.

Authorities said yesterday they are continuing their investigation of Kaplan, whose firm, with its motto "Specializing in Difficult Situations" has been in business since 1974.

If he is convicted on any of the charges, Kaplan's license as a private investigator could be suspended or revoked, said David Dick, executive director of private security services in the Virginia Department of Commerce in Richmond.

Dick, whose department regulates the state's 150 licensed private investors said yesterday that Kaplan's is the first such indictment of a private detective in Virginia in at least two years.

A curlyhaired man who sports a diamond pinky ring, Kaplan once told a reporter that he began his career by photographing adulterous couples in compromising situations. Kaplan said he charges clients about $150 for three-hour sessions.

Kaplan is scheduled to be arraigned Thursday in Arlington Circuit Court.