THE ASSASSINATION of president-elect Bashir Gemayel removes Lebanon's best hope of escaping from the agony it has endured for nearly a dozen years. "Bashir," as he was familiarly known, was himself no innocent. He had participated, as the leader of an important Maronite Christian militia as well as of his family's Phalangist political party, in the jungle that Lebanon became as a result of internal strife and external provocation and invasion in the 1970s. Yet there was good reason to believe that he had sobered and matured and that he was dedicated, as he put it on our op-ed page the day of his election, to "the unity of Lebanon; the uniqueness of the Lebanese experience; and liberty, security and justice for all Lebanese within a democratic government that guarantees all citizens' basic freedoms."

Mr. Gemayel was often tagged a "Christian rightist" who had earned the enmity of Lebanon's Moslems. It was an open secret that, as the intervening Syrian "peace force" in the mid-1970s became patrons of his rivals in the PLO and some of the Moslem militias, he had accepted substantial Israeli aid. Yet when the Israelis invaded Lebanon last month, he resisted the considerable pressure and temptation to join them in battle against his erstwhile foes. He was looking ahead to the need to run for president and to heal Lebanon after the war. For similar considerations of national consensus, he stood up to Israeli demands after the Beirut siege for a commitment to an early peace treaty.

In the parliament that elected him on Aug. 23, deputies came from 23 of Lebanon's 26 voting districts. Some 43 of 51 Christian deputies voted, presumably (no tally was kept) for him. Nineteen of the 41 Moslem deputies voted; if the one vote against and the four abstentions came from their ranks, that left him with 14 Moslem votes. Immediately thereafter he began a series of consultations with Moslem leaders.

"The people of Lebanon must agree that force has no place in the inevitable disagreements that arise with any country," he wrote on the op-ed page. "Lebanese pluralism, which has tended in its self-assuredness to overlook occasional resort to violence, must evolve to place a new emphasis on the peaceful settlement of disputes." Now he is a victim of the violence he had come to deplore. From his death some will conclude that the rebuilding of Lebanon is beyond human reach. It will also be observed that vengeance is sure to track any Arab leader who indicates he is ready to make peace with Israel. But Lebanon's latest tragedy cannot be allowed to darken the vista Bashir Gemayel had hoped to clear.