Maronite Catholics, the largest and most combative Lebanese Christian community, which is leading the fight against Syrian troops, may finally have picked the wrong patron after almost 900 years of securing foreign protection.

The meanderings of the last 3 1/2 years of violence in Lebonan should caution against any attempt at definitive answers. But the Maronites in their desperation the very alliance - with Israel - that could turn out to be fatal to their stubborn claims to power and leadership.

The Israelis' failure so far to come meaningfully to the Christians' aid in the current round of fight suggests that the Maronites badly misjudged their most recent protector's willingness to jeopardize other goals, such as the Camp David accords, for the sake of a foreign ally. Thursday's gunboat expedition is considered low-key by past Israeli retaliatory standards.

Maronites began their long their long history of foreign alliances within a century of being driven from the Orontes River Valley in Syria and taking refuge in the Mount Lebanon fastness which remains their heartland. In what critics term their first betrayal of Moslem Arabs, they welcomed the invading Crusaders in 1099.

Ties with the Vatican - and with ever more powerful and wealthy Western European - had begun a half-century earlier, when the Maronites chose Rome over the weakening Greek Orthodox hierarchy in Constantinople when Christendom's eastern and western wings split in 1054.

The religious association developed into a cultural political and sentimentical arrangement that helps explain why many Maronites think of themselves as Europeans as much as Arabs.

Yet historians describe them as Arab. Their church literature from the earliest documents of the 9th century on are in Arabic. Their liturgy follows the Syrian rite.

The Maronite church and its three monastic orders waxed rich. Even today the church and orders are considered the biggest landowners in Lebanon. But tensions with rival Druza Moslems provoked a wholesale massacre of Maronites in 1860 on which as many as 20,000 Maronites were slaughtered.

France, which for several centuries had encouraged the Maronites and helped their education, stepped in and forced the Ottoman Empire to grant Christians special privileges. The Christians proposed - the Greek Orthodox, Greek Catholics, later the Ar refugees - but none so much as the self-confident, active Maronites.

When France began its League of Nations mandate over Lebanon and Syria in 1919, the Maronites were convinced their day had come and that Western influence under the French would be eternal. In fact, it lasted only until 1943, when under British pressure France was obliged to grant Lebanon independence.

Even during the period of their most protected status, the Maronites made errors for which they would pay dearly later. In 1920 they sided with France against Emir Faisal, who was defeated by French arms in efforts to install himself as king of Syria as a reward for helping the allied war effort against Turks.

That Maronite decision was considered a crime against Arab nationalism - as was their later sympathy, which blossomed into an informal alliance, with Israel.

Another misjudgement that has cost the Maronites was their success in persuading France to add to the original area of Lebanon the agriculturally rich Beqaa Valley and north and south Lebaono. Although no official, undisputed census has been taken since 1932 - it showed a 51.2-48.8 percent breakdown in favor of the Christians - the addition of those taditionally Moslem lands with their higher birth rate helped tip the demographic balance against the Christians.

But under the government system bequeathed by the departing French, the Marnoties controlled the bureaucracy. Under the so-called National Covement of 1943 the Moslems accepted lesser posts and a clause guaranteeing Christians a 6-5 ratio in the National Assembly.

Even without the approximately 400,000 predominantly Moslem Palestinian refugees in Lebanon, social scientists now estimate that the Christians of the resident Lebanese population.

The first signs of Moslem rebellion against entrenched Christian privilege came in 1958. In that civil war, the United States landed Marines to preserve the status quo, threatened by help to the Moslems from President Gamal Abdel Nasser.

In Maronite eyes, the Americans had replaced the falling French protector. But oil and shifts in the atmosphere of diplomacy had changed the U.S. attitudes significantly by the time a new civil war broke out in 1976. The Maronites misread the retrenchment of American power and its unwillingness to commit troops abroad after Vietnam.

The Maronites fought first alone against the Palestinians and their leftist Lebanese allies, then alongside Syria against those same foes when they proved too threatening, and now finally against Syria with Israeli help.

Pessimists see signs of Maronite decline at nearly every turn. The majority of Lebanese who have emigrated since the fighting started in April 1976 have been Christians - often the elite. The Syrian artillery pounding of East Beirut is destroying the bases of Maronite power: the schools, hospitals, grand homes and business that traditionally set the tone for the country.

Perhaps the Maronites' most serious error was insisting that they had won the 1975-1976 civil war. The Moslems and Palestinians have long ago conceded. But the Maronites were convinced they had outmaneuvered the Syrians, whose help actually made the difference two years ago.

This outlook prompted them to take on the 30,000-man Syrian force when a hard look at the balance might have dictated avoiding a collision.

What the future holds for the Maronites, who are still roughly half the Christian population in this country of 3 million, is unclear. It is difficult to be optimistic. The magic of Moslem deference to Maronite-dominated institutions is fading, although a short period of outside help might turn back the clock.

Too much Moslem blood has been spilled by Christian hands - and vice-versa - to make such an outcome appear more than a temporary arrangement. Perhaps most telling is the silence of Moslem Lebanese, who do not approve of what the Syrians are doing but cannot bring themselves to forgive the Israei alliance and forget their own war with the Christians.