Playing down the political disputes and family feuds that have split them in the past, Lebanon's Christians are falling into line behind President Amin Gemayel.

Recent party elections have gone Gemayel's way with surprising ease, showing a consolidation of Christian ranks that runs counter to what had been widely predicted just six weeks ago.

The conventional wisdom after Pierre Gemayel, the president's father and the leader of the dominant Christian Phalangist Party, died of a heart attack Aug. 29 was that Amin Gemayel would become dangerously vulnerable to challenges from party hard-liners and from the rival Chamoun and Franjieh clans.

Instead, Gemayel and senior Christian party members have maneuvered swiftly to tighten political control and to fill key posts with people preferred by the president.

Working in Gemayel's favor has been an increased sense of threat among Lebanese Christians. The past year has gone badly for them. Dozens of Christian villages in the hills east and south of the capital were lost to Druze militia forces, and the Lebanese Army, a cornerstone of Gemayel's rule, disassembled in the face of a takeover of west Beirut by Shiite and Druze militiamen in February.

Many Christians feel abandoned by the West and Israel. Concerns about a precipitous Israeli withdrawal from southern Lebanon and worries about how new tensions between Syria and Jordan may play themselves out in Lebanon have deepened insecurities here and encouraged Christians to rally around Gemayel.

"Many people thought that after Pierre's death, Amin would be weaker," said Karim Pakradouni, a senior Christian militia adviser. "But Amin now has greater freedom of action and is having more impact in the party. He is consolidating his position step by step. If he succeeds, he can negotiate better" with Nabih Berri, leader of the Shiite movement Amal and Walid Jumblatt, the Druze leader.

While Gemayel's position has been bolstered, the president himself has stepped only rarely into public view in recent months. Aides say Gemayel is deliberately keeping a low profile to let attention focus on the Moslem warlords who joined a reconstructed national unity Cabinet five months ago.

But some Lebanese and western observers suspect Gemayel's lack of exposure reflects uncertainty about what he should say, given shifting regional alignments and the domestic political deadlock.

In any event, Gemayel is reported by associates to be busy behind the scenes patching up ministerial quarrels. He is also said to be spending more time than before on party affairs.

Syria has also lent its support to a closing of Christian ranks around Gemayel, figuring this will contribute to overall stability in Lebanon and foster a Christian-Moslem accord on political reforms.

Syria resumed the role of political godfather in Lebanon after the collapse in February of the U.S. peace-keeping effort. Gemayel's own tilt toward Damascus in late February stirred objections in the Christian camp among those who had looked to Israel to safeguard Christian rights in Lebanon. This resentment has waned, however, amid grudging acceptance that close cooperation with Syria is Lebanon's only practical option.

"It is a mistake to think Israel is an option for Lebanon," said Pakradouni, a former Phalangist Party politburo member who two years ago was promoting a peace treaty with the Jewish state. "The only practical option is Syria. Amin tried the Israeli option, and he tried the American option, and we saw the results."

Confronted by Moslem demands to relinquish political power, Christian officials say now is the time to solidify their own party organization. "There is a recognition in the party that we are passing through a difficult period," said Alfred Mahdi, a member of the Phalangist Party politburo. "What's important is that we create an institution around which to rally the community. We are trying to strengthen the Christian front."

Seen as the first test of this effort was the selection of Elie Karameh to succeed Pierre Gemayel as head of the Phalangist Party. A physician by profession, Karameh was little known outside the party bureaucracy. But insiders say that as an organization man he is well-suited to streamline the party apparatus, which will be his primary task.

A second more difficult test came last week with the election of a new leader of the Lebanese Forces, an alliance of Christian militias. Originally established as a military wing of the Phalangist Party, the 6,000-strong Lebanese Forces had begun to develop a separate political identity. There were fears its fighters would try to impose their hard-line views on the Phalangist Party.

Leading members of the Lebanese Forces, including commander Fadi Frem, who is married to Amin Gemayel's niece, openly opposed the president's swing toward Syria and the abrogation in March of the U.S.-brokered May 17, 1983, agreement on the withdrawal of Israeli forces from southern Lebanon.

They also balked briefly in July at pulling back their heavy artillery when the reconstituted Lebanese Army reasserted nominal control over the capital. Some of them have staunchly advocated partitioning Lebanon along Christian and Moslem lines, in opposition to Gemayel's insistence on reuniting the country.

At a closed-door vote Tuesday, Frem was replaced as commander by Fuad Abu Nader, the 28-year-old nephew of Gemayel. The new militia leader is expected to bring the Lebanese Forces back under party control and to be less likely to clash publicly with Gemayel, though some officials say the charismatic young military chief may prove more difficult for Gemayel to handle in the long run than was Fadi Frem.

Meanwhile, a much-publicized campaign has been launched against corruption, excesses and a lack of discipline in Christian party ranks. George Saadeh, Phalangist Party vice president, recently signaled an imminent purge of those undisciplined or unqualified members who escaped close screening during the war years.

Party officials say they have wanted to reorganize for some time but had to defer to Pierre Gemayel's authoritarian rule. "Under Pierre, it was hard to make changes," Mahdi said. "He was like a god. But we were all preparing ourselves for after his death. We moved quickly."

While this has benefited Amin Gemayel, the president still serves in the shadow of his idolized brother, Bashir. Many Christians continue to believe that Bashir, who commanded the Lebanese Forces and was assassinated in September 1982, three weeks after his election as president, would have made a more forceful and decisive leader. Posters of Bashir outnumber those of Amin in Christian-dominated East Beirut.

"The president is getting stronger, but the issue is not how to strengthen the president," Mahdi said. "The issue is how to solidify the Christians around the party so that they can survive this period. There is still resentment against Gemayel, but there is a certain recognition that whoever is president leads the Christians. The interest of the Christian community now is not to do anything that would jeopardize the president's position."

Aides to Gemayel say his top two priorities at present are securing the withdrawal of Israel from southern Lebanon and negotiating the deployment of the Lebanese Army to territories outside Beirut now held by militias. Some of his political associates worry about two problem areas that could disrupt an already shaky process of normalization.

One is the possibility of a hurried Israeli withdrawal that would not give Lebanese Army units time to take control in the Iqlim al Kharroub, the area between the Damur River south of Beirut and the Awwali River north of Sidon. The coastal edge of this region is controlled by the Lebanese Forces, which entered after the 1982 Israeli invasion. Dug into the hills farther inland are Druze fighters.

These rival militias have clashed repeatedly. A fragile cease-fire has been imposed by Israeli Army patrols, but each side is accusing the other of deploying heavy guns in preparation for a showdown battle once the Israelis withdraw.

A second worry is the repercussions for Lebanon of the struggle for influence between Syria and Jordan. It is feared that King Hussein of Jordan, after reconciling with Egypt last month in a move seen as checking Syrian dominance in the region, may try to weaken Syria further by stirring trouble in Lebanon, possibly inciting the Palestinians or the Moslem Brotherhood, a fundamentalist Sunni group opposed to Syrian President Hafez Assad. Alternatively, it is feared that Syria may move against Jordan, leading to some spillover conflict in Lebanon.