FBI agent James Cavanaugh yesterday refused to answer most of a House subcommittee's questions about overhead billings by Pratt & Whitney Aircraft Group, saying his superiors ordered him to do so because of a federal investigation under way.

Cavanaugh, who appeared under subpoena, said FBI Assistant Director Oliver B. Revell summoned him an hour before the hearing and directed him not to answer questions involving the 2 1/2-year probe of Pratt & Whitney or matters of FBI policy.

Cavanaugh, who heads the FBI investigation of a company plant in West Palm Beach, Fla., said he believes that the decision was made by the Justice Department.

The FBI's action came as a surprise to the Energy and Commerce subcommittee on oversight and investigations. Panel members said their staff had interviewed Cavanaugh and understood that he could testify about the Pratt & Whitney allegations as long as the questions did not involve secret grand jury testimony.

But when subcommittee members repeatedly inquired about Pratt & Whitney billings and lack of progress in the probe, Cavanaugh replied: "I'm not authorized to testify concerning the substance of the investigation."

"You're a government watchdog, and you were effectively muzzled," Rep. Ron Wyden (D-Ore.) told Cavanaugh. Subcommittee Chairman John D. Dingell (D-Mich.) said Cavanaugh had no legal authority to refuse to answer questions that did not involve grand jury proceedings and promised to pursue the issue with the Justice Department.

Later, retired Pentagon auditor George R. Spanton testified that he had found that Pratt & Whitney double-billed the government for more than $3 million in expenses. He said the company later acknowledged the error and repaid the money.

Spanton said Pratt & Whitney had charged the Pentagon for "outrageous overhead expenses" and compared its billings to recent disclosures of $244 million of improper expenses charged the government by General Dynamics Corp. He said several Pentagon officials who oversaw Pratt & Whitney later went to work for it.

Pratt & Whitney officials have said any questionable billings were corrected years ago.

But Spanton said the company has charged the government for excessive salaries, worldwide travel by executives' wives, transporting guests on corporate aircraft, lavish banquets, tuxedo rentals, babysitters, firewood, basketball tickets, country club dues, luxury cars, entertainment of government officials and such souvenirs as 4,000 baseball caps, 3,600 company pens and 3,500 tie tacks.

The panel also disclosed that the Defense Criminal Investigative Service has begun a probe of allegations that senior Pentagon officials violated the law by accepting gifts and entertainment from General Dynamics.