SAN LUIS OBISPO, CALIF., DEC. 10 -- A bitter final note, scrawled in ink on the back of a paper air-sickness bag, was found in the debris of Pacific Southwest Airlines Flight 1771, the FBI disclosed today.

"Hi Ray," the unsigned note began. "I think it's sort of ironical that we end up like this. I asked for leniency for my family remember. Well, I got none and you'll get none."

Investigators believe the note was written by David Augustus Burke, a recently fired USAir employe, to his former supervisor, Raymond F. Thomson, 48, of Tiburon, Calif.

Burke, 35, is believed by investigators to have smuggled a .44 Magnum revolver aboard the flight to seek revenge. Thomson, who lived north of San Francisco, regularly commuted on PSA to his job as head of USAir's office in Terminal One at the Los Angeles International Airport.

The two men were among 43 people, all those aboard, who died Monday when the commuter jet slammed into a hilly cattle ranch 15 miles northwest of here. The plane, a four-engine BAe146, exploded into pieces so tiny that they resembled broken oyster shells.

A .44 Magnum and six spent shells were found Wednesday among the wreckage. FBI documents filed in federal court in Los Angeles, including a search-warrant affidavit, reveal that Burke borrowed a Smith & Wesson .44-caliber revolver last month from a USAir coworker and was allowed to bypass a preflight weapons check Monday because he was "a familiar airline employe."

Meanwhile, police in Hawthorne, in southwestern Los Angeles County, said they received a report two days before the crash that Burke had threatened his estranged girlfriend with a revolver. The investigation received low priority, police said, because the woman made the report on a Saturday and did not want to press charges.

PSA spokesman Bill Hastings said that company officials were informed "by other sources" less than three hours after the crash that Burke by-passed security without credentials. He said the information was given immediately to the FBI. Under PSA rules, no one can bypass the checkpoint unless they show a badge and are in uniform.

Hastings said Ogden Allied Aviation Services has a contract with PSA to man the checkpoint. Diane Dressel, a secretary at Ogden Allied's Los Angeles office, said that she had "no idea" about the incident and that no one there was allowed to speak to reporters. An evening call to Allied's New York City headquarters was unanswered.

In the affidavit, FBI Agent Kevin D. Kelly said an unnamed PSA official told another FBI agent that Burke was waved past the checkpoint without being asked to show identifcation. Officials of USAir, which bought PSA in May, said they destroyed Burke's airport pass immediately after he was fired.

Investigators believe that Burke entered the cockpit, accounting for the sounds of a scuffle that can be heard on the cockpit voice recorder, according to a source who heard the tape and asked not to be named. Because of the tape's poor quality, investigators have had difficulty identifying all the voices and sounds. The tape is being enhanced at FBI headquarters.

The cockpit sounds are followed by a mechanical scream, which could indicate an acceleration. Witnesses have described hearing "shrieking" sounds as the plane plummeted to earth, nose first.

Tape-recordings of transmissions between air traffic controllers and the jet show that less than two minutes passed between the time the pilot issued an emergency call, reporting that he had heard gunshots, and the time the jet disappeared from the radar scope, according to the Federal Aviation Administration.

Richard T. Bretzing, special agent in charge of the Los Angeles office, said today that if Burke were alive, "we believe we have sufficient evidence to charge him with crimes aboard the aircraft."

Bretzing said the note was found by a volunteer from the San Luis Obispo County search team, and he described its condition as "readable." He said FBI forensic experts identified Burke's remains at about midnight Wednesday through a print on a finger.

The FBI affidavit said Burke borrowed a .44 Magnum from Joseph Drabik, a colleague and longtime friend. In an interview Tuesday with FBI Agent Michael Mahoney in San Francisco, Drabik said Burke came to see him "three or four weeks ago, in November . . . " and seemed "depressed."

Burke, who worked at Los Angeles International Airport, was fired Nov. 15 for allegedly stealing $69 in in-flight liquor-sales money and was fired Nov. 19.

The affidavit said Burke met with Thomson at the Los Angeles airport on Monday at 12:30 p.m. local time. Flight 1771 took off at 3:32 p.m.

The affidavit reports that Burke left a last message to his estranged girlfriend, Jacqueline Camacho, on her answering machine before he boarded the PSA flight: " . . . Jackie, this is David. I'm on my way to San Francisco, Flight 1771. I love you. I really wish I could say more, but I do love you."

Camacho retrieved the message at 9 p.m., nearly five hours after the crash.

Hawthorne police reported that Camacho, 33, told them two days before the crash that Burke threatened her and her 6-year-old daughter with a gun at 1 a.m. Friday after she drove into the underground parking lot at her apartment building.

Police Lt. James McInerny said the report, made at noon Saturday, was given low priority because it came in on a weekend and because she did not want him prosecuted.

Camacho told police that Burke, whom she had known for eight years, forced her to drive with him for several hours. According to police, she said she agreed to talk to him if he would leave the gun in the car. Camacho said he came into her apartment and showed her the bullets that he had not put in the gun, police said.

Camacho later told the FBI that Burke threatened her with a "dark, very big {revolver} with very big bullets" and told her he had obtained it from Drabik "to scare her into talking to him." She said Burke told her "Drabik didn't know why he needed the gun but helped him get it 'in good faith.' "

Drabik told the FBI that the revolver had an eight-inch barrel and that he gave Burke a dozen shells.

In the FBI account of its interview with Camacho, the child with her is identified as Burke's daughter, Sabrina, 12, not Camacho's daughter.

Although friends and relatives in Rochester, N.Y., Burke's home for almost all his life, said he occasionally fell into black moods and yelled at or threatened his children and girlfriends, he appears to have become particularly unstable in the weeks before his death.

According to court papers, the 5-foot-2-inch, 120-pound Camacho said that on Oct. 16 Burke, about 5-foot-8-inches and of husky build, "dragged me out of bed and to the living room and tried to choke me. He squeezed my throat until I couldn't breathe and then let go. He tried to do the same thing the following morning."

Her declaration was attached to an Oct. 22 temporary restraining order she obtained from Superior Court Judge Milton L. Most in Torrance, a community in southwestern Los Angeles County. She told the court that on Oct. 17, "I asked him to take his things and leave. On the 18th, he came back and cut the wire in my car that caused the car to stall out. He admits to doing that.

"Also on the 19th, he returned again and stole the garage remote opener that left me without access to get in and out of my garage. He cut up a few of my clothes and has admitted to doing all of the above," the declaration said.

The judge barred Burke from coming within 100 yards of Camacho or her home and also extended the same protection to a person identified as Nina Chung, thought to be Camacho's daughter. Burke worked with Camacho for several years at the Greater Rochester International Airport and told friends he transferred here to be near her, even though USAir had given the supervisor's job he wanted to someone else.

He had told friends he wanted to marry Camacho, although he had fathered seven children with five other women whom he had never married.

The FBI reported finding several legal documents during a search of Burke's three-bedroom townhouse in Long Beach.

Staff writer Jay Mathews and special correspondent Matt Lait contributed to this report.