The fate of more than 40 Americans held for the fourth day in the hijacking of Trans World Airlines Flight 847 grew more uncertain yesterday as Lebanese Shiite Amal leader Nabih Berri said he had ordered the hostages taken from the plane and adopted the hijackers' demands as his own.

U.S. officials expressed hope that Berri could help end the crisis but also acknowledged that it could drag on for some time.

Berri personally guaranteed the safety of the hostages, whom he said he had ordered removed from the plane because he feared bloodshed in the event of a rescue mission. However, there were indications in Beirut that at least some passengers and crew may still be on the aircraft.

"I am not a go-between," Berri said. "I am a party, and I and the Amal movement have adopted the demands of the hijackers" that hundreds of Shiites held in Israel be released. Their release, he made clear, was the key to resolving the crisis.

"I gave guarantees to the hijackers that I will not release the hostages or the passengers without the release of the . . . prisoners," Berri said at a press conference. "If Israel does not release them, I would say to the kidnapers, 'Now you take the people and do what you want,' " he added in a separate interview.

That rhetoric left little room for the kind of deal that Arab diplomats earlier had said might be possible: release of the Americans in return for a credible pledge that Israel would release the Shiites soon afterward.

The possibility that the Americanshave been taken off the plane and into Beirut suggested that what began over Athens Friday as a classic hijacking may be turning into more of a hostage-taking. U.S. officials became decidedly less optimistic late yesterday about the prospects for an early end to the crisis. "I don't see any immediate resolution of the situation," one administration official said.

American officials reiterated that the United States would not ask Israel to release the Shiites it holds, on the groundsthat this would be a concession to terrorists. Israeli officials repeated that they would consider releasing the Shiites, but only in response to an official, public U.S. request. Some U.S. officials expressed irritation at Israel's position.

"The plane is an American plane. The hostages are American citizens, and the crew is an American crew," Israeli Minister of Police Haim Bar-Lev said. "We need not take any intitiative." Israeli officials indicated that a request by the Red Cross for the release of the prisoners would not suffice.

The State Department's latest count put the number of hostages at 43, held in three groups: three, most likely the crew, believed to be still aboard the plane; 30 possibly taken off the plane early yesterday, and 10 whom the hijackers picked out as having Jewish-sounding names and taken from the plane during an earlier landing in Beirut.

The body of the passenger shot in the head early Saturday and thrown out of the plane in Beirut was identified as that of Robert Stethem, 23, of Waldorf, Md., a U.S. Navy diver attached to an underwater construction team based in Norfolk.

National security adviser Robert C. McFarlane telephoned Berri early yesterday and told him that he "has in his hands the ability to end the hijacking," the White House said. Secretary of State George P. Shultz said, "Hijacking and other forms of terrorism are unacceptable in a civilized society. We call upon those holding hostages to treat them properly and release them immediately."

The Marine Corps said its Mediterranean Amphibious Ready Group departed from a port call at Gibraltar yesterday morning and is now deployed in the Mediterranean. A spokesman said the departure was scheduled and not related to the hijacking. He declined to disclose the course if the group, which consists of 1,800 to 2,000 marines aboard three vessels.

The government of Spain yesterday rejected a demand by the hijackers that it release two imprisoned Lebanese Shiites.

In London, the International Federation of Airline Pilots Association urged a boycott of the Athens and Beirut airports because of the hijacking, which the association blamed on lax security.