But an equally compelling drama was quietly unfolding behind the scenes.

A day after the hijacking began, Italian air-traffic controllers were stunned to see a blip representing another TWA jet disappear from their radar scopes. They feared a crash, not knowing that a complicated exercise in deception was being executed by TWA and high U.S. government officials. In order to simulate a disappearance, the TWA pilot being dispatched to the scene had deliberately switched off the radio beacon signaling his position. Then he turned his jet toward a rendezvous with an American commando force.

TWA and the commandos were to jointly prepare an assault on the hijacked jet to free its hostage passengers and capture - or kill - their captors. To enhance the mission's secrecy, a TWA executive says, ''We made our plane over Italy disappear into thin air.''

TWA's ACCOUNT

The assault plan, which eventually had to be aborted, is one of many details that has gone unreported despite the wide coverage the hijacking received. Many details remain classified secrets.

But TWA has carefully documented its own role in the effort to end the hijacking, in which one American passenger was killed. The airline's internal report, supplemented by interviews with many airline and government officials, offers a case study of airline behavior in a hijacking. Details of a world-wide manhunt for the hijackers are also beginning to emerge.

To some extent, the tale is one of misadventure. Diplomats thought negotiations in Algiers would end the hijacking after three or four days. Thus, State Department officials badly wanted to keep the plane there.

Their wish was frustrated. The hijackers bluffed their way out of Algiers by faking the screams of a tortured ''victim'' to extort needed fuel. Then, John Testrake, the captain of the hijacked jet, deliberately feigned engine failures to ground the jet at Beirut - the last place that TWA and U.S. officials wanted it. Finally, some of the traps later set for the hijackers were sprung on empty air.

SCREAMS REVERBERATE

The TWA episode also shows the anguish experienced by airline executives when events halfway around the world spin out of their control and unthinkable horror suddenly invades their working day. While one TWA passenger was being savagely beaten in Beirut, for example, the plane's radio was left on and the transmission was recorded. Hours later, TWA executives in New York listened to the recording, including the victim's screams.

''It was a nightmare,'' says C. E. Meyer, who was the president of TWA at the time. ''The whole thing was a nightmare.''