President Amin Gemayel has finally decided on the so-called ''Arab option.'' By flying to Syria Wednesday, apparently ready to tear up Lebanon's US-orchestrated pact with Israel, the Lebanese leader has moved sharply away from American efforts to secure peace in the region.
And, as diplomats were quick to point out, the trip also means Syrian President Hafez Assad has won another round in the regional struggle to establish influence in Lebanon, defying two years of effort by the United States to squeeze Damascus out of the picture.
There is strong evidence that turning to Syria was Mr. Gemayel's least-favored option. Diplomats and local officials say Gemayel was forced to turn to Syria - the Soviet Union's closest ally in the Mideast - after the US and Israel turned down requests over the past two weeks to help his beleaguered regime hold off further assaults from opposition forces. Two presidential advisers dispatched to Jerusalem and Washington reportedly were bluntly told there was no enthusiasm for fresh efforts to get more deeply embroiled in the Lebanese quagmire.
Gemayel's visit, his first to Syria since he took office in September 1982, was the first step of a Saudi-mediated plan to end nine years of civil war by reconciling the Christian-led government with the Syrian-backed opposition.
Lebanese officials said Assad and Gemayel would discuss:
* Stabilization of a cease-fire between government forces and Muslim and Druze militias, including the possibility of deploying United Nations troops to replace the mostly departed multinational force.
* Normalization of relations. This is significant because Syria has never formalized diplomatic ties with the territory that was historically part of ''Greater Syria.''
* The Israeli-Lebanese troop withdrawal accord signed May 17, 1983, and the Israeli occupation of southern Lebanon.
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