D.C. Mayor Marion Barry said yesterday that he believes U.S. Attorney Joseph E. diGenova has wiretapped his phones and bugged his home, and challenged diGenova to issue a public denial.

The mayor offered no evidence to confirm his suspicions, or any documentation to support the assertion that any bugging took place. Barry said he has had more than one private sweep of his home that indicated bugging and wiretapping, but said no records were kept of the inspections, with the technicians instead giving oral reports.

Meanwhile, some experts in electronic surveillance said yesterday that it would be virtually impossible to conclude that listening devices were actually being employed, based on the kinds of tests that likely were done for Barry. The experts said the only way to be sure is to find the device, and apparently no search for devices was made at Barry's home.

Appearing on radio station WOL (1450 AM), Barry said there were "forces" that did not want him in office and challenged diGenova to state categorically that authorities had never bugged Barry's home, office or car from 1979 -- when he took office -- to the present.

DiGenova's office declined comment specifically on Barry's challenge, referring instead to a statement on Wednesday in which prosecutors said they had not been the source of any surveillance referred to by Eddie T. Dockery, an electronics specialist who told a federal grand jury that he had found evidence of wiretapping and bugs at Barry's home beginning in 1984.

"{Federal} law enforcement officials have placed no such devices in such locations during the time period alleged by Mr. Dockery," diGenova's Wednesday statement read in part.

Told about the U.S. attorney's decision not to elaborate further, Barry said, "A 'no comment' means they did it." Barry has filed suit in U.S. District Court attempting to challenge diGenova's handling of a widespread investigation into allegations of corruption in District government contracting.

Dockery, 33, was arrested yesterday on a felony warrant for allegedly writing more than $10,000 in worthless checks to buy cellular telephone equipment. Barry said Dockery's legal trouble does not undermine the work he did.

"I've had additional work done to confirm {Dockery's} work," Barry said. "This is a highly sophisticated business -- vibrations off the window. I have it done periodically. I started out with little Mickey Mouse things, Dark Ages, {a} beeper that I bought myself." Barry said he has since allowed private firms to use more sophisticated gadgetry.

Barry, both in his radio appearance and a later interview, said he made a personal decision not to find the source of the bugging devices because he is doing nothing wrong.

"The only thing it could cause me concern about, particularly, a very delicate subject, is in my bedroom in terms of personal conversations that Effi and I may have, personal activities that I may have," Barry said in the radio appearance.

Talking to radio show host Cathy Hughes -- who a day earlier had excoriated Barry for not showing up for a scheduled appearance -- the mayor repeated previous assertions that he has been investigated "more than anybody I know of . . . . "

"There are forces out there that don't particularly like what I do, how I do it, or who I stand up to . . . . I have a different style and I suspect there are people in this town and this country who don't want us to maintain leadership in the nation's capital."

Asked about the quotes later, Barry suggested that he was talking about black leadership generally rather than himself personally. "It's a group" that's unpopular, he said. Asked what "forces" were arrayed against him, the Democratic mayor suggested they included "conservative Republicans."

Security specialists were skeptical of the eavesdropping sweeps apparently conducted for Barry. They questioned the logic of the account by city-hired consultants who said they used sophisticated electronic equipment to conclude with "90 percent certainty" that the mayor's house was bugged, but who then did not physically search for the bugs themselves.

The independent eavesdropping experts interviewed said it is virtually impossible to determine the presence of listening devices with electronic equipment without finding the actual bugging devices.

Electronics specialist Dockery told reporters that he and the security company for which he sometimes works, A. Mele and Associates, started finding convincing evidence of audio surveillance of Barry's home and car telephones, but followed Barry's orders not to search for the listening devices themselves. Repeated tests since then have strongly suggested they are still working, Dockery said.

Ray Jarvis, an eavesdropping expert who owns Jarvis International Intelligence Inc. of Tulsa, said that even the most skilled specialist cannot conclude that there is a listening device simply by using electronic testing equipment on a telephone line.

"There's absolutely no way a person can tell if it's a telephone tap without examining it," Jarvis said. He added that the testing equipment cannot distinguish between a phone tap, a crimp in the telephone cable or a point in the cable where various lines are joined.

The Mele firm was hired by the city for an unknown amount to conduct the sweeps. Dockery and the firm's owner, Anthony Mele, have declined comment about the precise type of testing equipment used. But based on vague descriptions of the equipment provided by Dockery, Jarvis and others surmised that they may have employed two pieces of sophisticated equipment.

One is called a reflectometer, a device costing about $7,000 that is used by the telephone company and airlines to test for obstructions or interference in cables. The device shoots an electronic pulse down a telephone line leading away from a home or office, then measures the returning pulse. The echoing pulse can give an indication of the distance of the obstruction, and its type, specialists said.

Specialists said it appears another device used is a radio frequency spectrum analyzer, which measures signals of various sorts, such as radio and television signals, and filters them out. Analysts search for indications of other signals, from devices that transmit bugged conversations to nearby receivers.

Jarvis said his firm and many others in the field of "eavesdropping countermeasures" refuse to work for clients unless they say beforehand that, in the event a device is found, they will take it to law enforcement officials.

But Joel Kaplan, another bugging expert who owns the D.C.-based Action Investigative Services Inc., said that one is not obligated under law to take evidence of a bug to authorities. He said that occasionally people who discover bugs will leave them in place to feed incorrect information to the listener, performing a "double whammy."

Kaplan said that he has worked on bitter divorce cases in which a person finds that a spouse has placed a bug, then leaves it in place and arranges to have a made-up conversation with a divorce lawyer to confuse the opposition.

Kaplan added that he found it hard to understand why the sweepers would fail to try to find a bug they suspected of being there. "If I said that, the client would say, 'I'm putting a stop payment on your check.' "

Yesterday Mele said that he also had been questioned by federal investigators about the consulting work his firm did for the city. Mele and Associates performed the sweeps under a purchase order, an arrangement similar to a contract but for less than $10,000.

Mele said that he had turned over to authorities all the firm's bills and invoices on work for the mayor.

Dockery, of 1820 Kalorama Rd. NW, was arrested yesterday at the business where he works, BCD Cable Corp., in connection with the writing of worthless checks amounting to $10,200 last spring, D.C. police said. Authorities said a Columbia electronics company, Public Phone Centers, filed a criminal complaint that Dockery had bought at least five cellular phones by writing a check on a BCD account that had been closed several months before. Dockery resold the phones to a number of people, said representatives of Public Phone Centers.

BCD Cable officials could not be reached for comment.