Beirut — A dangerous split has emerged among Lebanese President Amin Gemayel's own support community - the Maronite Christians. At odds are the politicos, who have generally if reluctantly backed the peace effort, and the younger generation of militia fighters, who provide on-the-ground leverage for the Phalange and other Christian parties.
The right-wing Christian militia is upset by the regime's announcement Monday that it is cancelling its security accord with Israel. This militia, called the ''Lebanese Forces,'' has threatened to sabotage the new peace effort in Lebanon, as well as undermine the Gemayel government.
The Lebanese Forces rejected the cancellation, calling it a ''decision of subjugation imposed by a Syrian offensive against the free Lebanese people.'' More ominously, it called for mobilization of all Christians for a ''resistance campaign'' that will ''secure freedom, security, and honor'' for Lebanese Christians, once the dominant segment of the population but now a minority. It described resistance ''against Syrian dictates'' as a ''holy duty.''
The threat is particularly significant since it shows that President Gemayel has lost yet another sector of the population, one that was a main element in his personal power base.
During the first seven years of civil strife, before his election in 1982, Mr. Gemayel served as a top commander in the Lebanese Forces.
Pierre Gemayel, founder of the Phalange and father of the President, said last week he felt the Lebanese Forces could be brought into line by putting the squeeze on its leader, Fady Frem. But nevertheless, Mr. Frem pledged that the militia was prepared to take matters into its own hands.
''The Lebanese Forces will play a major role no matter what situation evolves now,'' he said. ''If Gemayel wants to remain President, he will have to deal with this new fact. In the Christian area, there is something new that has come up. . . . Now we will be having our own political visions and options.''
According to Western diplomats, the militia has recently remobilized its troops in east Beirut. This breaks an agreement with the government to keep armed men off the streets of the capital.
And last week, the militia underwent a major shake-up in the command structure. This was interpreted as part of a consolidation to make the Lebanese Forces an autonomous power, capable of operating separately from Christian political parties.
The Christian militia can also count on support from thousands in southern Lebanon, who are particularly fearful of being overwhelmed by the dominant Muslim population in this Israeli-occupied area. They have become increasingly vocal at demonstrations and rallies in support of close links with Israel.
Christian hard-liners, who traditionally have had military and political backing by Israel, are afraid they might come under Syrian rule because of Gemayel's decision to adopt the so-called ''Arab option.'' They do not trust pledges last week by Syrian President Hafez Assad that he will guarantee the safety of the various Christian sects.
Christian militia leaders point out that the Syrian peacekeepers first came to Lebanon in 1976 to protect the Christians, but subsequently switched sides and fought the Lebanese Forces.
The Syrians will not have a direct representative at the national reconciliation talks, scheduled to begin in Lausanne, Switzerland, on Monday.
But they can effectively play the role of spoiler back home if the militia decides to foment trouble through military sabotage. Such violence would heighten tension between Christians and Muslims and violate the still unofficial cease-fire.
Christian moderates are also hinting that they do not fully back Gemayel's course of action. Former President Camille Chamoun, the second most powerful Christian party leader, announced Tuesday that his National Liberal Party will play the role of ''constructive opposition.''
The Christians' complaints against Gemayel are also likely to play a major role at the Lausanne talks. They provide a new reason for this minority to demand guarantees for itscontinued prominence in government now that the opposition Muslims have wrung a concession for Lebanon's alignment with Syria and the Arab world, rather than with Israel and the West.