A House subcommittee chairman charged yesterday that top Reagan administration officials "capitulated to the gun lobby" by ducking a scheduled appearance to testify on a bill to ban undetectable plastic guns.

Rep. William J. Hughes (D-N.J.), chairman of the Judiciary subcommittee on crime, said officials at the Justice, Treasury and Defense departments barred their subordinates from appearing before his panel to present the administration's position on the bill.

Hughes said top administration officials told his subcommittee they were unable to reach a position on the legislation, a stance Hughes said was at odds with earlier supportive statements made by federal firearms experts.

Hughes said administration officials gave no reason for pulling out of the hearing, but he suggested the reason was obvious.

"The only thing we can conclude . . . is that it appears the administration has capitulated to the gun lobby," he said. "It's just a sad commentary. I have been here 13 years and I've never seen such a shocking display."

Hughes said his hearing was particularly timely in view of reports that the recent crash of a Pacific Southwest Airlines jetliner in California was caused by a disgruntled former employe who boarded the plane with a gun described as a .44-caliber Magnum pistol.

"As the headlines this week have so graphically illustrated, getting a handgun on a plane leads to massive tragedy," he said.

"The administration's refusal to cooperate in the legislative process, because of what appears to be an effort to appease one isolated, narrow special interest, is creating the impression that it is selling out the safety of the traveling public and the airline industry."

The National Rifle Association and other gun groups have opposed the legislation as unnecessary, saying no undetectable all-plastic guns are on the market. They acknowledge that partially plastic guns are available, but say they have enough metal in them to be recognizable by current metal detectors.

Backers of the legislation say undetectable plastic guns will be available by next year and that a ban is needed at least until effective detection devices are developed.

The Federal Aviation Administration says it is 10 years away from having detection equipment for plastic guns, but contends a U.S. ban is not a solution because such weapons still could be obtained in other countries.

Airline industry groups strongly support the legislation as do virtually all major law enforcement groups, but the NRA prevailed in a recent Senate vote on the issue.

While the administration has taken no position on the bill, Hughes said weapons experts in the Treasury's Bureau of Alcohol, Tobacco and Firearms and the Pentagon's Office of International Security Affairs had previously voiced concern about the future availability of plastic guns.

"The staff of the assistant secretary of defense for international security affairs told our staff that they wanted to testify, that they support the legislation because they are very concerned about what they perceive as a very real threat these weapons pose in the hands of terrorists," Hughes said.

"But at 4:30 {Wednesday} afternoon, we were notified that the Defense Department witness was instructed not to testify, reportedly by Deputy Defense Secretary Howard Taft," Hughes said.