Shiite Amal movement leader Nabih Berri today arranged the release of three more captives taken off a hijacked Trans World Airlines plane and appealed to the U.S. government to pressure Israel into freeing more than 700 Shiite Lebanese prisoners.

At a press conference at his apartment, Berri presented the three: Greek pop singer Demis Roussos; his American companion, Pamela Smith, and Arthur Targontsitis, 18, a Greek-American student from Brockton, Mass. They were turned over to the Greek ambassador and later left by ship for Cyprus.

The release of the three today reduced the number of hostages still held in the five-day-old crisis to 40, but questions remained about where and under what conditions they were being kept. And at least a hint of tensions between the hijackers and Berri's men surfaced.

Berri would not confirm publicly that passengers had been taken off the aircraft in two groups, some with Jewish-sounding names early Saturday and 30 other passengers late Sunday or early Monday.

"There are no American Jews, they are all Americans," Berri said, in response to a reporter's questions. However, he has said privately that there were two groups being held in areas under his control.

It would be difficult for Berri to confirm openly that he is protecting American Jews, given the pressure he is under from extremists in his own community and Syria.

Berri said the crew was among those taken off the plane, although there were reports that the captain, John Testrake, was back aboard. Air traffic controllers at Beirut's airport said they had had no contact with the pilot, although the plane has shifted position since Sunday morning.

Targontsitis said he was held in a group of five. "I was with a group of other people I assume to be Americans . . . . I was with my group, a group of five."

Roussos said his captors were polite and had treated him well. He said that he sang for them and that they gave him a cake for his 40th birthday. "I had some good moments," Roussos said. He tearfully embraced a number of Amal militiamen before leaving in a limousine with Smith and the Greek ambassador.

Berri, who is also justice minister and state minister for southern Lebanon, complained that he got involved in the affair out of a sense of duty to help the Americans, while they, in turn, were reluctant to nudge Israel toward releasing the Shiites, rounded up during Israel's occupation of Lebanon. Berri has adopted the hijackers' demand that prisoners held in Israel in Atlit be released.

"Why does the government of the United States not interfere to save 700 innocent people and open the road to save the 40?" he asked.

Berri, accusing the U.S. government of making no serious effort to resolve the five-day hostage crisis, said the hostage drama would end in 24 hours if Washington would pressure Israel.

"Why don't you, the American people, intervene with the American government to save the 700 innocent people? You have to pay taxes every day to support Israel, so you have the right to ask Israel to free those people," Berri said.

"I am sure that if your government asks Israel this little thing, to save those innocent people from jail, this will probably finish in 24 hours."

Berri stressed that the ball was now in the American court. He added that he had been touch with the International Committee of the Red Cross, the United Nations, and the ambassadors of France, Britain and Spain.

Asked if he did not feel awkward, as Lebanon's justice minister, detaining innocent civilians, Berri protested that those in Atlit were also mostly civilians. He said they included farmers, teen-agers and villagers who were in line to donate blood at a hospital when Israeli troops seized them in south Lebanon.

Berri has said repeatedly that he will wash his hands of the entire affair and hand the hostages back to the hijackers if there is no progress in the negotiations.

Berri told reporters that the passengers of TWA Flight 847 were being kept in different locations by Amal in Beirut. He said he was personally supervising their menu and sleeping accommodations to make sure that they had "an acceptable way of life."

Sources said they believed the passengers were taken off the plane in Beirut in two installments, early Saturday morning during the aircraft's second stopover in Beirut, and at dawn Sunday.

The hijackers, who had the plane flown to Beirut three times during the saga, released more than 80 passengers during two stops in Algiers.

Well-informed sources said 11 were taken off the first night and that this may have included the three released today. Berri insists that he has access to all of the hostages, which he estimated to number 40.

He said the move to let the three go today was a "good-will gesture."

In the control tower half an hour before Berri's press conference, Amal representative Bassam Tleiss urged the hijackers in the airliner to give permission for the release of the three on "humanitarian grounds" and because the Greek government had responded to their plea to free their comrade, Ali Atweh.

After 20 minutes of consultations and a tirade against the Americans, the hijackers accepted.

During the conversation with the hijackers, one of them insisted that Greece must promise to press Spain and the United States to pressure Israel into releasing the Shiite prisoners.

"We want clear actions," he said. "This thing has lasted too long. It is not possible to stay like this."

The note of impatience suggested that the hijackers might be starting to feel like hostages themselves, as they wait on the plane they commandeered. The hijacker warned Tleiss that the exception was only for the Greeks and for "no one else." He said the "plane is 15 meters away from the airport, and if I want I can crash it into the terminal building."

Two Shiites held by Spain on charges of attempting to murder a Libyan diplomat in Madrid last September, and whose release is also demanded by the hijackers, are scheduled to go to trial Wednesday. Berri said yesterday that he had talked the hijackers into dropping a demand that Shiites held in Kuwait be freed. However, this had not been known to be among the hijackers' early public demands.

The hijackers continued to order large quantities of food and demanded that maintenance men clean the aircraft.

Berri has received phone calls from Syrian President Hafez Assad and Vice President Abdel Halim Khaddam during the past two days. Syria is the preeminent force in Lebanese affairs, and the Lebanese government has not had much impact on the hijacking.

Prime Minister Rashid Karami brushed the crisis aside as a "reaction to the injustices taking place against this region and its people," reflecting the general hostility to Israel and its main backer, the United States.

Karami resigned in April in protest over sectarian fighting, and has remained in President Amin Gemayel's national unity government as a caretaker.

In recent weeks the ineffective government has not been able to meet to discuss Lebanon's successive crises, let alone influence events here.

The virtual absence of Gemayel from the scene in Lebanon in recent weeks has dramatized both the basic lack of government in the country and the emergence of Berri as perhaps the leading political figure and military power because he heads the Amal militia.

Druze leader Walid Jumblatt, the transport and public works minister, has admitted that he is unable to ensure airport security.

Berri today announced that his militia was ending the siege of Palestinian refugee camps south of Beirut as part of a Syrian-brokered plan to end a month-old war between Shiites and Palestinians.

The accord, announced late yesterday in Damascus, is not described here as a victory for Berri. As the bloody Shiite-Palestinian war dragged on, Syria became aware that Berri had to cut his losses and it is argued that he chose this time, while attention is focused on the hijacking, to make it public.

The accord calls for a cease-fire, the collection of heavy guns from the camps and the withdrawal of Shiite Amal fighters and the Lebanese Army's 6th Brigade besieging the Palestinian camps.

Berri said the truce was being discussed by a special committee including a Syrian military observer, representatives of the National Palestinian Salvation Front and Lebanese groups allied with Syria.

The truce would allow relief missions to go into the camps immediately to evacuate the wounded and deliver food and water supplies to residents trapped inside.