By most measures, Nabih Berri, leader of the Shiite Moslem Amal movement in Lebanon who has become a central figure in the TWA hostage drama, would seem to be the Lebanese leader with the best chance of helping find a solution to the grim, complicated TWA hostage crisis.

The most influential Shiite leader in Lebanon, he also has strong family ties to the United States, where his six children were educated andhis American-born former wife now lives. In the past he has had friendly relations with Washington, which also has expressed the hope that Berri can spearhead a solution to the hostage problem.

But the crisis that the 46-year-old lawyer and politician now finds himself at the center of could wind up harming rather than helping his often tenuous claims to the leadership of Lebanon's long-downtrodden but now militant Shiite community.

Confronted by both the Shiite hijackers of Flight 847, who apparently are not from his own mainstream Amal militia, and by the Israeli and U.S. governments stressing their refusal as a matter of principle to give in to terrorism, Berri has much to lose -- and seemingly little to gain -- by intervening in the fate of the American hostages.

On the one hand, he will be blamed by the United States if he is unable to bring the hijacking crisis to a satisfactory conclusion -- the more so if the episode ends tragically.

On the other, in a region where dealing with the U.S. government will win him scant credit, any achievement in freeing the hostages -- even in exchange for his coreligionists held in an Israeli prison -- already has been discounted by his aggrieved public in Lebanon, in part because of Israeli indications, prior to the hijack, that they intended to release the prisoners soon.

Despite his formal titles as leader of Amal and and Lebanon's minister of both justice and South Lebanese affairs, his hold on the rival forces struggling for domination of Lebanon's largest religious community has never been all-encompassing.

But if the turbulent course of events in Lebanon has eroded much of the moderation that once made him an exception in a country of volatile warlords, Berri cannot be considered a Lebanese Ayatollah Ruhollah Khomeini, determined to humiliate the United States.

Over the past decade, Berri has had to confront fellow Shiites as much as the Christians and other Lebanese communities, not to mention the Israelis, Palestinians, Syrians and Americans who at various times have sought to manipulate or radicalize his majority community.

Berri's long friendly relationship with the United States -- he holds an alien's residence permit and reportedly visits family in the Detroit area frequently -- cooled at an official level as various U.S. policies, such as ordering the Sixth Fleet shelling of the Beirut area in 1983, gradually made him increasingly wary of the administration's intentions.

In 1981 he laughed off accusations in the United States, apparently inspired by Christian Lebanese militia intelligence, that he was behind a purported Libyan "hit squad" out to assassinate President Reagan.

He could afford to do so because Amal has not been on genuinely good terms with Libyan leader Muammar Qaddafi since the movement's founder, Iman Musa Sadr, mysteriously disappeared while visiting Libya in 1978.

It was the Imam Sadr's disappearance that brought this lawyer-lieutenant to the forefront of Amal, which grew out of Sadr's efforts to develop a voice and a focus of power for Lebanon's Shiites.

But Berri soon faced challenges to his leadership, which persisted through Amal's victory in taking over West Beirut in February 1984. And the Shiite "national resistance," which effectively hurried the Israeli armed forces out of South Lebanon, was not entirely his.

For its part, Syria encouraged the Iranian-influenced Hezbollah -- or Islamic fundamentalist "Party of God" -- which sought to take over Amal's militants.

Recently, Berri's efforts to bring to heel Palestinian guerrillas in three besieged Beirut refugee camps have not added to his prestige.

He is seen by many as doing Syria's bidding as much as trying, for his own purposes, to prevent the Palestinians from again becoming a military force in Lebanon.

In the present situation, Berri is both arbiter and party to the TWA hostage crisis.

His predicament helps explain why he has backed the hijackers' key demand for the release of more than 700 Shiites held in Israel.

His U.S. ties enable him to understand that the American public is unlikely to see those prisoners' fate as comparable to that of the TWA hostages, a comparison he reiterated today in Beirut.

But that is how many Shiites and other Lebanese see their plight, and they make the further point that in removing them from their own country, Israel acted in defiance of the Geneva Conventions.

Indeed, many Lebanese believe that Israel is holding the Shiite prisoners as virtual hostages to ensure quiet in the border strip it mans with advisers to the Israeli-supported South Lebanese Army.

And they also observe that the SLA itself took hostage 21 Finnish soldiers of the United Nations Interim Force in Lebanon (UNIFIL).

Moreover, Israel, in their view, considerably weakened its once firm policy of publicly refusing to deal with those it considered terrorists when last month it exchanged 1,550 mostly Palestinian prisoners for three of its soldiers captured in Lebanon.