Amin Gemayel, elder brother of slain president-elect Bashir Gemayel, was overwhelmingly elected today to be the next president of Lebanon.

Gemayel, 40, a dapper businessman and member of parliament from his father's Christian Phalangist Party, was elected on the parliament's first ballot -- gaining 77 of the 80 votes cast.

The election, unlike that of Gemayel's brother last month, went smoothly and rapidly after Speaker Kamal Assad delivered a brief eulogy for the late president-elect and declared a three-minute silence in the temporary chamber at the Faradiyeh military barracks of East Beirut. A large picture of Bashir Gemayel was hung with black drapes.

The president-elect, who is to take office Thursday on the expiration of President Elias Sarkis' six-year term, broke into tears when his election was announced. He then went to the dais to deliver an impromptu speech calling on all Lebanese to unite behind him to resolve the grave crisis that Lebanon is facing.

Gemayel did not mention that his country is still occupied by Syrian, Palestinian and Israeli troops nor did he refer to the killing of hundreds of Palestinians last week in Beirut's Shatila refugee camp--a massacre that eyewitnesses have declared was conducted in part by units of his late brother's Christian militia.

He talked of needing to fill the "vacuum" left by his brother's assassination, in a bomb explosion at a Phalange party headquarters in Christian East Beirut.

"Bashir Gemayel is calling on us," the president-elect told the parliament and the nation as he cradled a microphone. "It is not a time to despair. It is a time to unite, to unify the Lebanese, to save Lebanon."

The election appeared to be conducted in a sense of mutual purpose among deputies from the Christian and Moslem communities. Gemayel said it was "a first step" toward "rebuilding Lebanon."

In contrast to the election of his brother and every past president in memory here, there was none of the gun firing with which Lebanese mark events of joy or sorrow. Gemayel had warned before his election that he did not want anyone to fire guns that would offend his family's mourning.

The election was proof that after the nation's recent trauma, there is a concerted attempt by Christian and Moslem alike to seek unity after more than eight years of intermittent, often savage, civil war.

While a majority of the country's important Moslem leaders had sought to block the election of Bashir Gemayel last month by boycotting the election in Parliament, today these Moslems -- led by the crusty former prime minister Saeb Salam -- trooped in and gave their vote to Amin Gemayel.

Salam, who had led the boycott, hugged the assassinated president-elect's brother when he arrived in a rush of heavily armed bodyguards. Salam walked down the aisle arm-in-arm with the future president, as the assembled deputies applauded. This seemed to support the assertion that the politicians are hoping to revive the unwritten national pact of 1943, a rigid division of powers between Christians and the Moslems.

The most somber person at the election was the president-elect's 77-year-old father, Sheik Pierre Gemayel, who founded the rightist Phalangist Party in the 1930s after having been impressed by Nazi youth groups during a visit to Berlin for the 1936 Olympics.

The elder Gemayel sat on the front bench, with his son and former president Camille Chamoun, who has variously been a rival and ally.

The two dominant Maronite Christian clan leaders sitting side by side symbolized the quest for unity not only with Moslems but within Christian ranks. The task of imposing such unity, by force of personality as well as persuasion, could be the new president's greatest challenge.

It is a challenge that the Lebanese people had expected to fall on Bashir, who at 34 was the former commander of the Christian's Israeli-trained Lebanese Forces militia. Bashir's strength and firm nationalism had begun to win over Moslem rivals before his death. Some have said this was because he seemed determined not to be forced into signing a peace treaty with Israel.

The more supple, moderate and tradition-oriented Amin Gemayel must now face Israeli pressure for a peace treaty, which Israel has said will be a price of their withdrawal from Lebanon. That is to come after agreements are reached, through U.S. mediation, for withdrawal of Syrian and Palestinian combatants in the eastern Bekaa Valley and the north.

Gemayel quietly opposed his younger brother's earlier tacit alliance with the Israelis. A treaty now could be expected to antagonize the Moslems who make up more than half the 3 million population. Gemayel is said to be counting on U.S. diplomatic support to counter Israel's demands, and occupation.

More problematic for Gemayel will be whether he can impose his leadership on the militia that his brother had forged as a personal instrument of power. There are signs that militia commanders who were loyal to Bashir Gemayel have broken away from Phalange party influence since his death to become a force of their own.

The charge that units of that militia conducted the massacre in Shatila camp last week has presented Gemayel with a critical challenge of his authority even before he takes office. Gemayel and the party have officially denied any involvement in the Shatila massacre.