That President-elect Bashir Gemayel should now be mourned as Lebanon's last great hope for peace is no more than a measure of that tormented nation's desperate state. Gemayel's conversion to conciliation and coalition with his old Moslem enemies and his rivals in the Christian community came largely after his election. The odds were long on his ability to resolve old scores and establish a strong central government, even if he had survived Tuesday's bombing.

But that is precisely the point: his conversion, however expedient, was real. His reaching out to establish a government of "reconciliation" was having its intended effect. Perhaps most important, the Begin government in Israel was beginning to recognize the damage it was doing to Gemayel's fortunes by its excessive embrace.

It is against all this that the loss of Gemayel has to be measured. And the real measurement is to be found not so much in characteristically generous, retrospective eulogies as it is in the particular insight of one of the last Americans to talk to Gemayel just a few days before the assassination.

The American was Sen. Arlen Specter (R-Pa.), who had taken off for Lebanon last weekend on behalf of the foreign operations subcommittee of the Senate Appropriations Committee to examine that country's need for U.S. economic aid. His account of his whirlwind, three-day passage is well worth examining for what it says about how the stage was set before Bashir Gemayel was killed.

Specter says he found the 34-year-old Gemayel hard-pressed and "very nervous" about a crucial meeting he had later that day with Saeb Salam, an elder statesman of the Sunni Moslems. He had the quality of "the right man at the right time," the senator felt. Gemayel did not want to talk about aid; he seemed to be counting on help from Saudi Arabia and Kuwait. What he needed was "time," and this meant getting Israel to back off on its insistence on an immediate peace treaty.

Specifically, Gemayel urged Specter to use his influence on Menachem Begin; to explain that Israeli pressure was undermining Lebanon's claim to independence, endangering its relations with other Arabs, and undermining his efforts to "forge a national coalition."

Convinced that Gemayel was "making all the right moves" (the U.S. Embassy agreed), Specter met the next day with Begin in Jerusalem. It was an evening session in Begin's upstairs study. But Begin was adamant at the outset. He spoke of Gemayel's "ingratitude"; he was impatient for a peace treaty, irritated -- and expansive on Lebanon's historic importance to Israel.

But after lengthy discussion of Gemayel's problems, Begin softened. He finally promised Specter, in so many words: "I won't press him."

Immediately afterward, Begin came down to his living room and repeated that pledge publicly. There is confirming evidence that the Begin government, after smothering Gemayel with a crushing embrace, had indeed decided to cool it a little.

Had the damage already been done, in a way that weakened Gemayel and even may have contributed to Tuesday's violence? Specter emphatically rejects the notion. Given the slim chance that Gemayel's assassins will ever be clearly identified, this theory of the case is no more worth pursuing than Israel's theory (wholly unaccompanied by any evidence) that the PLO was responsible.

More interesting to the senator is the sense he had that, with Gemayel, there was at least some hope of Israeli restraint, of a reasonably prompt withdrawal of Syrian as well as Israeli forces from Lebanon, and of the establishment of a workable Lebanese central government.

He came away with the impression that Begin saw Lebanon as "a place he would not like to be in, but also doesn't want any trouble from." Begin did not see the Syrians as a problem. He was "very blunt" about the probable impact on the Syrians of Israeli artillery trained on Damascus. He believed that with some face-saving, the Syrians would be more than willing to leave.

In short, Specter returned from his trip sharing the conviction of White House experts and State Department officials that with a special U.S. envoy back on the scene, and "reconciliation" beginning to work, the Lebanese crisis just might be beginning to be soluble. Now with Gemayel's death, just about everybody agrees that all bets are off -- on Lebanese "reconciliation," on the Syrians, on the behavior of Israel.

Echoing the State Department's grim assessment, Specter concludes: "We are back to peg one."