Were it not for the intervention by the many foreign powers involved in the Arab-Israeli conflict, the Lebanese would long ago have established the first genuinely secular parliamentary state in the Arab world. The defeat of secularism is the real tragedy in Lebanon, for it has barred from power the forces for moderate political reform in the Arab world that could best guarantee the long-term security of Israel.

This is because Lebanon is the Palestine Liberation Organization's last Arab sanctuary, and the outcome of the civil war will determine the character of the Palestinian leadership in the coming decade. This, of course, is of paramount importance to Israeli strategists who acknowledge that Anwar Sadat alone cannot guarantee a cessation of Palestinian guerrilla attacks. Rhetoric aside, the Israelis know that any comprehensive peace is contingent upon reaching some accommodation with the Palestinians.

True, Prime Minister Menachem Begin has sworn never to deal with the PLO. But, despite resistance from some Arab and Israeli quarters, President Carter can now legitimately argue that the Camp David accords provide the framework for a comprehensive peace precisely because they guarantee a Palestinian autonomy and the creation of a West Bank self-governing authority through free elections. Many Israelis who refuse to deal with PLO leaders based in Lebanon would not object to negotiations with elected Palestinian representatives.

This can't happen unless an alternative Palestinian leadership - more moderate and reconciled to gradual step-by-step sovereignty over only a very small portion of "Palestine" - emerges from the Lebanese conflict. In all likelihood, the moderate wing of the PLO can survive only if the Lebanese civil war is resolved within a secular context.

There are three possible outcomes to the present Lebanese crisis:

A partition of Lebanon into Moslem and Christian states.

A revision to the "confessional" (religiously oriented) political system that existed before the civil war.

The creation of a secular parliamentary state.

Most observers agree that the partition of the country advocated by the extreme right-wing Christian militia would lead to interminable bloodshed. But Israeli strategists did toy with this idea during the 1975-76 civil war, because, with Lebanon partitioned into religious mini-states, Israel would no longer be a theocratic anomaly in a sea of Islamic countries. The greatest problem from the Israeli point of view is demographic. The Christian state would lie in the northern Lebanese mountains, while the hostile Moslem state would border Israel. So while the Israelis would like to see the Christian militias maintain their autonomy, Israel today is opposed to a Lebanese partition.

Even the extreme-right Christian militias no longer support partition. Today they believe themselves powerful enough to dominate the entire country - if the Syrians would leave and the PLO could be disarmed. These Christian extremists would like to reestablish the country's archaic confessional system of government whereby political power is apportioned strictly on a religious basis. That system has always worked to the advantage of the Christian minority, which possesses a majority in parliament and therefore traditionally controls the presidency.

But neither Lebanon's Moslem majority nor its poor Christian urban communities can again suffer the kind of economic discrimination and political authoritarianism that prevailed under the confessional system. Nevertheless, because the Moslem majority is supported by the PLO, the Carter administration has been tempted to ignore the secular option and back the confessional system in the hope that the Christians will disarm the PLO.

Such an objective is hopeless; guns are too easy to come by in the Mideast arms bazaar.

Instead, the Carter administration should seek ways to bolster the political position of the moderate PLO factions within Lebanon as part of a secular state.

Regardless of the political risks, this solution should be viewed with optimism for several reasons. It would pave the way for a shift throughout the Middle East away from religious fanaticism and narrowly based confessional regimes. Also, a secular and democratic Lebanon would exercise a moderating influence over the PLO, and would treat its Palestinian refugee population with far more sympathy than would a confessional Lebanon dominated by Christian commercial interests.

Further, should the comprehensive settlement promised by Camp David become a reality, a majority of the Palestinians now in Lebanon would choose to remain there, rather than resettle in a West Bank "state."

Most important, a secular Lebanon would greatly strengthen the hand of the moderate factions within the PLO leadership. And the extremists would be hard pressed to challenge the sovereignty of a Lebanese government that was truly representative of all Lebanese.

The biggest obstacle to a secular solution has always been foreign interference on one side or the other. Left to themselves, the Lebanese are quite capable of building exactly the kind of democratic government that is in the best interest of Israel's long-term security.