Members of the crew that piloted TWA Flight 847 said yesterday that they believe their hijackers killed Navy diver Robert Dean Stethem partly out of frustration at the difficulty of communicating their demands, and the copilot said he felt some responsibility for the serviceman's death.

"I felt almost partially responsible because I was unable to get . . . their demands across to the people at Beirut for fuel and just to get communication, understanding how desperate the situation was," said Philip Maresca, 42, of Salt Lake City, who pressed Beirut airport officials for fuel and landing rights early in the 17-day ordeal.

Speaking at a news conference with Maresca and other crew members, Capt. John L. Testrake, 57, said the two original hijackers were "very much afraid of something going wrong" after learning that the plane would have to stop in Beirut for fuel. They began beating Stethem, he said, "to get us to demand fuel."

The news conference and interviews with returning hostages revealed more details of their captivity, ranging from new reports of the abuse endured by Stethem and fellow diver Clinton Suggs to a tale of Massachusetts car dealer Ralf Traugott's nocturnal travels around Beirut with a collegial Shiite militiaman.

Also yesterday, TWA employes were evacuated from the company's headquarters in New York for 30 minutes because of a bomb scare, triggered by the arrival of two packages addressed to Testrake and Maresca and labeled: "Do not X-ray: cassettes."

A New York City bomb-squad team was summoned to open the parcels, only to find that they contained tape recordings of patriotic songs and accompanying sheet music.

A TWA spokesman said the tapes were intended as an admiring gesture to Testrake and Maresca. Police said the songs had been composed recently and referred to the hijacking and hostage-taking.

As the hostages spent their first full day on American soil, several disclosed secrets, kept from their captors, that they believe saved their lives. Michael (Brad) Brown, 27, of North Miami Beach, whose honeymoon was interrupted by the hijacking, hid the fact that he was Jewish, according to fellow hostage Peter Hill, 57, interviewed on CBS News' "Nightwatch" program.

"There was no reason to suspect he might be Jewish," Hill said. "None of us did until we were on board that C141 in Damascus after being freed and he leaned over and told me. And I just felt such a great sense of elation . . . . We put it over on 'em! And the kid was just great."

Former hostage Jack McCarty, 40, of San Francisco said he and Victor Amburgy, 30, his traveling companion and roommate, hid their homosexuality from the Shiite Moslem militia for fear that they would be killed.

McCarty, a volunteer counselor for dying AIDS patients, told the San Francisco Examiner that he and Amburgy pretended to be brothers. The two had their arms around each other when they met President Reagan yesterday after a special TWA flight from Frankfurt to Andrews Air Force Base.

The gesture, he said, was an expression of their homosexuality, although neither had told his parents. Said McCarty, whose family lives in Boston: "When they found out, they flipped. Being 'out' in New England and being 'out' in San Francisco are two different realities."

While some hostages returned with tales of terror, Traugott, 32, told of developing a curious camaraderie with an Amal Shiite militiaman with whom he spent four days and three nights touring Beirut, drinking tea in a deserted alley, visiting a posh apartment where he was invited to fire a machine gun out the window (he declined), seeing a military command post and attending a funeral in the middle of the night for a slain Shiite militiaman.

"For me, it was a hell of an experience. Every day there was something new," the car dealer from Lunenburg, Mass. told the Beverly Times. "He took me out and showed me around day after day, night after night," Traugott said. "I told him I wanted to see this town. He took me uptown and downtown, in the city and in the country. He liked me because I expressed an interest in what was going on."

Traugott identified his escort as a man named Akal whom he believed to be second in command of the Amal militia.

But he and others also talked of previously undisclosed terrors. Traugott said soon after the hijacking, one of the hijackers held a gun to his forehead and a grenade next to his right ear and asked if Traugott was nervous.

At the pilots' news conference, Testrake said the hijackers brought Stethem and Suggs to a section behind the cockpit, tied them up and "beat on them quite severely" using an arm wrench from one of the crew chairs.

They "would jump on them with all of their weight, on their bodies repeatedly," Testrake said. "Initially, they did it to draw our attention to the fact that they were desperate men, that they were determined to have their way and that we should do exactly as they said."

The plane was hijacked en route from Athens to Rome, and made two trips between Beirut and Algiers before returning at last to Beirut, where the hostages were removed. Testrake said at one point, on the ground in Algiers, he was tempted to throw one of the hijackers out the cockpit window. But he said he was certain that the gunman's accomplices would have destroyed the plane.