BEIRUT, Lebanon -- Newly arrived U.S. warships carrying 1,800 Marines cruised off Lebanon Saturday as Shiite Moslem leaders warned Washington against 'muscle-flexing' and threatened to return 40 American hostages to the hijackers of a TWA jetliner.
Ghassan Sablini, the No. 3 man in the Shiite militia Amal, said the hostages would be handed back in two days if there is no movement in negotiations over demands that Israel free 764 Lebanese Shiite prisoners in exchange for the Americans.
But he later backed off the rigid deadline, saying, 'We said a couple of days but we were not specifying exactly 48 hours.'
'If we see our mission is not successful in the coming days and there is no advancement in a couple of days, then we will have no choice but to hand the hostages back to the hijackers,' he said.
Amal, Lebanon's largest Moslem militia, has been holding most of the 40 hostages in secret locations around Beirut, but four or five are thought to be held by Hezbollah, a pro-Iranian Islamic fundamentalist group believed to have initiated the hijacking June 14. The group has denied involvement.
Sablini's comments came after sources in Washington said three ships carrying 1,800 members of the 24th Marine amphibious unit linked up sometime Friday with a naval task force led by the nuclear-powered aircraft carrier USS Nimitz.
The arrival of the helicopter carrier USS Saipan, and two landing ships, the USS Nashville and the USS Spartanburg County, brought to seven the number of American naval vessels stationed off Lebanon.
The sources said the Marines were brought in as a 'show of force' but there were no indications they might be used in an attempt to rescue the hostages.
A Beirut radio station, the Christian Voice of Lebanon, said U.S. F-14 warjets made two pre-dawn sweeps over the Lebanese capital trying to pinpoint the locations of the hostages. The Pentagon denied the report.
President Reagan held a luncheon meeting at his Camp David, Md., retreat with Vice President George Bush and national security adviser Robert McFarlane to review the situation. There was no immediate word on the outcome.
Police sources in Beirut said Amal gunmen had deployed anti-aircraft batteries around the city's airport and southern suburbs in a move to preempt any attempt to rescue the hostages.
Thirty-seven passengers taken off the plane early last Monday were being held in secret locations in mainly Shiite southern Beirut. Reports on where the three-man crew is being held have varied, with some saying they are being kept on board the plane while others say they have been lodged in Beirut.
The jetliner with Capt. John Testrake at the controls, Saturday taxied to a refueling point to take on fuel for auxillary engines that provide power for air conditioning. It then parked about 200 yards from the main terminal.
The crew of the TWA jetliner requested a doctor to board the plane and armed hijackers were seen searching the man's medical bag before he boarded.
The doctor, who wore a white coat, said one of the American crew members suffered a painful bee sting, Britain's Independent Television Network said.
ITN quoted the doctor as saying the hijackers and the crew members were getting along 'quite well' and the atmosphere seemed friendly.
A Pentagon spokesman said he had no information on charges by Amal chief Nabih Berri that the United States has deployed troops in mostly Christian east Beirut. There are believed to be an unknown number of U.S. military advisers to the Lebanese army in east Beirut, but it was not known whether it was these men to whom Berri was referring.
Berri, who is also Lebanon's justice minister, made his comments in a statement in which he also said there had been no progress in negotiations on resolving the crisis.
Referring to local reports tha4 the U.S. naval task force had moved closer to the Lebanese coast, Berri warned in his statement the Reagan administration against shows of force, saying they would only make matters worse for the hostages.
'The American move seems more like muscle-flexing rather than logic and calm,' he said. 'Such things will bring great harm to the American passengers and United States interest not only in Lebanon bud in the whole region.'
Berri has taken personal responsibility for the hostages and is backing the hijackers' demand that the 764 Lebanese Shiites imprisoned in Israel be released in exchange for the Americans.
The Shiites were rounded up by Israeli troops during their withdrawal from southern Lebanon and transferred to Atlit prison near the Israeli port of Haifa.
The crisis began June 14 when two men believed to be members of Hezbollah -- Arabic for Party of God -- commandeered the TWA jetliner after it left Athens for Rome. They forced the pilot to fly several times between Beirut and Algiers, releasing most of the estimated 150 passengers each time the plane landed.
The aircraft landed for a third and final time in Beirut last Sunday and the remaining passengers removed sometime early Monday morning.
