Three passengers flying first class jumped a would-be hijacker Tuesday night, twisted his right arm back between his shoulder blades, slammed him against a bulkhead, locked his throat in a two-hand grip and then bound him hand and foot for delivery to federal authorities in Houston.

Yesterday, despite stern warnings that other passengers should not try doing the same thing, the airline, the FBI and the self-appointed passenger sky marshals were delighted with the outcome.

Pan American World Airways Flight 925, Houston-bound from Miami, was the second in two weeks to be saved from hijacking by irate passengers. Nine flights have been diverted to Cuba this year, and Tuesday's hijack busters--a laid-off Pan Am food manager, his teen-age son and a Miami trial lawyer--said they didn't aim to be part of the 10th.

"I figured, 'I may go but I'm not going without a struggle, pal,' " said Ralph Symons, a 225-pound attorney who jumped from his seat to help wrestle the skyjacker to to the deck.

The struggle began at 7:10 p.m. Tuesday, 20 minutes into the flight, with the Boeing 727 about 120 miles east of St. Petersburg.

A man identified by federal authorities as Alfredo Ayala, 30, a Cuban national described as agitated, strode rapidly from coach into the first class cabin, followed by flight attendant Fernando Villalobos, who told federal officials he thought the passenger was looking for the bathroom.

Witnesses said Villalobos opened the bathroom door for Ayala, who was fumbling with the entrance to the cockpit. The hijacker, announcing in Spanish that he intended to conducir--drive--the plane himself, kicked the bathroom closed and pushed Villalobos away.

At this, Spicer Lung Sr., a laid-off Pan Am food manager who sat in the first row, leaped up, grabbed Ayala's arm, twisted it behind him nearly to his neck, and said Ayala would take the plane "sobre mi cadaver," "over my dead body."

At that point, Lung Sr. said yesterday, the hijacker stopped twisting the locked cockpit door and lunged for the main exit, with its pressure-locked lever and bright red "DANGER" sign. Lung slammed the hijacker into a nearby bulkhead and called his son, Spicer Lung Jr., 15, for help.

The junior Lung, a 5-foot-11, 140-pound yellow belt in karate, grabbed the hijacker in a two-fisted strangle-hold from the front, nearly lifting him off the floor. Then Symons joined in.

"Suddenly this guy was contending with three virile American males," Symons said. "I think we hurt him. I feel a little sorry for him today. We probably put a little more energy into it than we should have."

Meanwhile, the pilot had flashed a hijack-alert signal to the radar screens back in Miami.

Within six minutes, Spicer Lung Sr. had bound the skyjacker hand and foot and strapped him into the left front seat of the airplane.

When the plane landed nearly two hours later in Houston, five U.S. marshals took Ayala into custody.

He was arraigned yesterday on two felony counts of attempted air piracy and interfering with a flight crew. FBI officials said they found no weapon on him.

"The only thing running through my head," the senior Lung said, "was, 'This will not occur if I can avoid it.' "

"I feel satisfied with what I did, but I don't think everybody should attempt what I did unless they are fully aware of the situation and have evaluated it," he said. "There were no visible weapons in his hands, and I took advantage of that."

Mike Clark, a Pan Am spokesman who confirmed that Lung had been laid off as supervisor of catering services on July 15, echoed Lung's warning yesterday, but added, "We have informed him this morning that we will find a job for him.

"We do not encourage passengers to get involved in matters of this sort, but in this particular case Mr. Lung saw a situation, he appraised it, determined what he was going to do, did it, and did it well. We are proud of him," Clark said. Fred Farrar, a spokesman for the Federal Aviation Administration, said, "We're not going to bad-mouth anybody, but if we had our druthers these things would be handled by flight crews who are trained in the proper handling of a hijacking," he said.

Trained flight crews, at least, probably would have been a bit gentler on the hijacker, Symons conceded yesterday. "I didn't feel all that disposed to read him his civil rights," Symons said, adding that the three passengers had been "pretty hostile" and had refused to allow the bound man a trip to the bathroom.

"I think he was happy to get to the FBI."