A Transportation Department task force recommended last year that airlines consider requiring their employes to pass through metal detectors to reach restricted passenger boarding areas.

But the task force also suggested that airline workers could be exempted from metal detectors if the airlines tightened their procedures for checking employe identification badges.

That procedure drew renewed scrutiny yesterday as authorities tried to determine how a former airline ticket agent could have carried a weapon onto the commuter jet that crashed Monday, killing all 43 people aboard.

Department officials and airline safety experts argue that the federal rules -- if enforced -- should have prevented David A. Burke from boarding Pacific Southwest Airlines (PSA) Flight 1771 with the handgun discovered yesterday in the airplane's muddy wreckage.

If Burke boarded as a passenger, he should have passed through a metal detector and surrendered any carry-on baggage for X-ray or hand search; if he boarded as an employe, he should have passed through a metal detector or had his identification examined and verified.

But the discovery of the weapon underscores the vulnerability of even the best safety systems to mechanical malfunction or human error -- the potential for boredom or familiarity to lower the guard of the individuals responsible for enforcing the rules.

This is particularly a problem with the private firms hired by the airlines to perform passenger security screening, an occupation characterized by low pay, minimal training, monotonous work and high turnover.

One possibility is that Burke may have been waved through security by former coworkers who knew him by sight and were unaware that he had been terminated, several aviation sources speculated.

If Burke carried a gun onto the plane, "it's a screw-up," said Richard Lally, vice president for security with the Air Transport Association, an airline industry group. "It's not because the procedures are wrong, it's because someone screwed up."

Burke worked for USAir for 15 years until Nov. 19, when he was fired for misappropriation of funds. Authorities are looking into reports that Burke had threatened to kill his former supervisor, Raymond F. Thomson, who was among the 38 passengers and five crew members who died in the crash.

Burke bought a one-way ticket and traveled as a passenger, not an airline employe, said Libby Fraser, a spokeswoman for PSA, which was acquired by USAir in May.

All passengers were screened before boarding; the screening equipment was inspected after the crash and found to be working properly, Fraser said.

When Burke was fired, USAir confiscated his employe identification badge and destroyed it, a company spokesman said. He would not have been issued a separate ID card by Los Angeles International Airport, where he had worked and where he boarded the PSA flight, an airport spokeswoman said.

Burke did not have to return his airline uniform, said David Shipley, a USAir spokesman. Shipley could not say whether Burke had surrendered his flight pass, a document that allows USAir employes to fly free on a space-available basis.

The Federal Aviation Administration has come under fire from Congress for the laxity of its rules in the past.

In June 1986, FAA inspectors reported that Washington-Dulles International Airport could not account for as many as 25 percent of the 9,000 identification badges issued to employes there.

At the same time, screeners at Dulles failed to detect almost 25 percent of the mock weapons hidden in carry-on luggage, airline officials reported during congressional hearings on the matter.

Two months later, the transportation secretary's Safety Review Task Force issued its first recommendations that airlines tighten up employe security. The stricter procedures were to include recording an employe identification in a log, or closely inspecting and verifying the ID card, to prevent workers from simply waving a card at a friend, one source familiar with the report said. The recommendations went into effect earlier this year.

On Tuesday, the FAA directed the nation's airports and airlines to "reemphasize and strengthen" procedures for regaining the ID cards of former employes and informing security personnel when a worker is fired.