The rising star of Nabih Berri, unlikely leader of Lebanon's rag-tag Shiite militia

A somber Nabih Berri paused for thought as he sat at the head of a long table in his stark apartment. Hordes of journalists waited for his view as to whether Lebanon's Christian President should resign in exchange for peace with the Muslims.

Mr. Berri's response reflected the depth of his political commitment:

''After what happened in the southern suburbs, (President Amin) Gemayel asked to give a speech. So I wait myself like a little child in front of his father. I wait to see at least one word that he is sorry about more than 100,000 - they are out from their houses. . . . More than 70,000, they went to the south. Living under the Israelis is better for them than living under the Christian Phalangists.''

''So I don't hear 'sorry.' Well,'' he paused again, ''I will see that he is sorry.'' He referred to the fierce fighting in the Shiite suburbs south of Beirut earlier this month, blaming the destruction on the Lebanese Army.

Angry and embittered, the leader of Lebanon's Shiite Muslims and their Amal militia has gone on the offensive. He threatens to bring down the Lebanese government unless there are radical changes that will give Muslims and Druze a greater share of power in a government long dominated by minority Christians.

Mr. Berri is an unlikely leader, as a Western diplomat noted: ''The major figures have always emerged from the important families, the clans, or because they are prominent clerics. Berri is different. He is a self-made man.'' He referred to such families as the Gemayels and Jumblatts.

A European diplomat said, ''Mr. Berri has also never been considered a radical. More than all the others, he tried peaceful channels first. He really tried to open a dialogue with the government. He still went to Baabda (the presidential palace) when the others had given up. And several times he was convinced he had Amin's promise, then nothing happened.

''He is not a revolutionary by any means. . . . His commitment is fully to the cause of the underprivileged, which in this country means the Shiites. . . . Throughout 1983, Mr. Berri pledged, 'I am for the legal authority. I don't ask to be president.' But in a warning the government did not heed, he also said: 'There will be no security without our rights.' ''

Berri has long been a moderate by Lebanese standards. Shortly before the recent fighting began, there was speculation that his following had dissipated to more radical Shiite movements because he favored negotiations over violence. He had already lost his key vice-president, Hussein Musavi, who in 1982 split with Amal to form the extremist ''Islamic Amal.'' Some reports linked this group to the bombing of American and French forces in Beirut last October.

But Berri's star is rising again with the victory last week of his rag-tag militia, outmanned and outgunned by the Lebanese Army, in west Beirut. Under his calm, decisive leadership life is almost back to normal in Muslim west Beirut.

This former lawyer has been the most underrated of Lebanese faction leaders, even though the Shiites are estimated to account for more than 1 million of the country's 3.5 million people. That is partly because the Shiites were not a major factor in the 1975-76 civil war and have only recently mobilized into an effective political and military force.

The Lebanese Shiites' former spiritual leader, Imam Musa Sadr, founded the ''movement of the disinherited'' in the early 1970s to politicize the Shiites. From this social movement evolved its military wing, Amal, which means ''hope'' in Arabic.

Many have recognized its potential. A European diplomat commented in 1982 that Amal held ''the decisive edge in any major future decision in Lebanon. Amal has not yet peaked. It is likely to become even more militant. They have nothing to lose by being so. Most of them have already lost everything of major value.''

Although it was Imam Sadr who rallied the Shiites, it has been Berri who organized them into a viable organization after the cleric disappeared in 1978 during a trip to Libya. A Lebanese political analyst evaluated the Shiite movement under Berri's leadership as ''the most politicized and combative of all sects.''

Berri explained, ''If you go by arms, ammunition, and equipment, we are probably the weakest party in Lebanon. . . . But our strength lies in our ability to make the people, the masses, carry out our orders. They do it because they know we are out to meet their needs.''

Amal's sympathy for the Iranian revolution has not helped its image. ''We support the Islamic revolution in Iran,'' Berri explained, ''but not on sectarian grounds, and we do not want an Islamic revolution in Lebanon. Our special relations with the Iranian revolution are based more on principles than on sectarian compatibility.''

Indeed, one of the biggest threats to Berri's future comes from the dozens of small extremist cells of pro-Iranian Shiites. Berri's recent successes have triggered speculation about the possibility of assassination attempts against him.

There is deep animosity between Amal and other Shiite groups. This was reflected last month when a Saudi diplomat was kidnapped. It was widely believed his abductors were Shiites.

An envoy who was with Berri when he heard the news described him as ''appalled and genuinely horrified.'' Berri, the envoy said, immediately ordered his men into the southern suburbs to set up checkpoints in the shantytowns and high-rises where the diplomat might be hidden, suspecting Shiite radicals were involved.

Rival groups accuse Berri of ''selling out.'' They like to point out that he holds an American green card, which will eventually make him eligible for United States citizenship. His ex-wife and children live in Dearborn, Michigan, where Berri visits at least once each year in part to keep his green card current.

Berri will have to wrest concessions from the government soon, if he is to hold on to his following. The younger Amal members are said to be frustrated by the lack of progress on the political front. Many who do not remember the days of coexistence with the opposition feel time has run out for moderation. If President Gemayel stalls further on reforms, it could cost Berri his credibility and radicalize the Amal irretrievably.

Perhaps ironically, Berri's demands are more advantageous to the Sunni Muslims and Druzes than to his own Shiites, since they involve no major shake-up in the division of power that would give the Shiites the speakership of the Parliament - the third highest job in government. He would also allow the Maronite Christians to retain the presidency.

''Whatever the events of the past two weeks, Berri is still the most reasonable of all the forces challenging this government,'' one of the few diplomats left in Beirut commented. ''Gemayel is a fool if he does not deal with Berri now. Otherwise it will cost him far more later.''