D.C. Mayor Marion Barry's police security detail decided earlier this year to purchase special equipment to detect electronic eavesdropping devices on the mayor's home and car phones, according to an internal police memo.

A ranking police official confirmed yesterday that Police Chief Maurice T. Turner Jr. had approved the purchase of the equipment, and said that the request for the devices came from the mayor's security detail.

"The security detail always has concerns," the official said. "They try to get everything they legimately need to do the job better."

He said the purchase of such equipment "is really a standard thing to do" to protect the mayor and his family and to ensure that their privacy is "not intruded upon."

Barry said yesterday that he doesn't know anything about the request. "I didn't request this equipment," Barry said. "I don't know if it's been delivered."

It could not be determined yesterday if the equipment has arrived or is in place.

The request for the equipment, which was contained in a Jan. 17 memo to Turner, comes after Barry expressed irritation at a continuing series of city government corruption investigations led by the U.S. attorney's office and the FBI.

The mayor and his supporters contend that these inquiries are part of a campaign to undermine Barry, who has not been implicated in any wrongdoing.

Barry and City Administrator Thomas Downs, who also said he was unaware of the equipment request, said that such security precautions would have nothing to do with any federal investigations.

Downs said the mayor does not get involved in decisions about his security and relies on the police to decide those issues. "Everybody around here is sensitive to the security for the mayor," Downs said.

Martin L. Kaiser, an electronic surveillance expert whose clients have included the Central Intelligence Agency and the U.S. military, said the telephone detection equipment sought for Barry is aimed at uncovering hidden devices that use a telephone and its lines to pick up conversations in the room where the telephone is located.

According to the memo, the two requested units, based on catalog prices, would cost less than $1,500.

Kaiser and other law enforcement experts said such equipment is virtually useless for detecting court-authorized telephone wiretaps employed by the FBI and other law enforcement agencies. Kaiser said legitimate wiretaps are hooked up at the telephone company's central office and cannot be detected by the equipment intended for Barry's phones, which is called a "telephone modulation detector."

The modulation detector is designed to detect changes in a telephone's electrical frequency, but those changes do not occur when the wiretap is installed through the phone company, Kaiser and other experts said.

According to the police memo, which is signed by Lt. Ronald Harvey, the head of the mayor's security detail, "One of the most important areas of responsibility is to have the security equipment capable of keeping the Mayor's telephone conversations secure."

Harvey and Lt. William White III, the police department spokesman, both said yesterday that the department does not comment on the mayor's security.