Once upon a time there was a Third World country that had been ruled by the French. The country's elite spoke French, were frequently Christian and looked to Paris as their cultural capital. In time, the French pulled out, the country fell into civil war and the United States came and tried with its soldiers to impose order and restore the authority of the cental government.

It sounds like Vietnam, but it isn't. It's Lebanon.

The Vietnam analogy gets wearisome, I know, and it is often used inappropriately -- Central America, for instance -- but Lebanon is looking more and more like a road we have been down before. All you have to do is substitute the name of Amin Gemayel for that of Nguyen Van Thieu and we are off in a time machine, once again being asked to buttress a central government that may lack popular support and being asked to do it again with money, material and American soldiers.

There are some differences, of course. There has been an interregnum between the French mandate over Lebanon and Gemayel's recent request for additional American troops, reportedly as many as 65,000. But Lebanon remains a trap. The country has shown the capacity to suck in one outside power after another, forcing them to take sides in the endless sectarian wars between Christians and Moslems and even between various factions of the same religion. This happened to the Ottoman Turks and later to the French and still later to the Syrians who, after all, first came into Lebanon as the saviors of the Christians -- only to later turn against them.

Now the same thing has happened to the Israelis. Their quick incursion into Lebanon has turned into an occupation almost sure to last a year. Israel not only must maintain the refugee camps but it also must support the private armies (like the one of Maj. Saad Haddad) that have enlisted on its side. By degrees, Israel is sinking into the morass of Lebanese politics.

But Israel, for all its concerns, is not America. Only America is locked in a world-wide struggle with the Soviet Union -- a struggle that has intensified as a result of the Reagan administration's foreign policy and the predictable reaction of the Soviets. Now we have Soviet Premier Brezhnev downplaying detente and telling the Cap Weinbergers of his military apparat that they can get all they want -- declaring, in the process, his intention to deal with American "adventurism." What better place to do that than the Middle East, a region where the Soviets have lost both influence and prestige?

Things are bound to heat up. A heightened American presence in Lebanon, a danger in and of itself, could produce a similar Soviet commitment to its Middle East client, Syria. Already there are 1,200 American troops in Lebanon. If the Soviets reciprocate on behalf of the Syrians--who, after all, have their own interests in Lebanon -- we will have done nothing but transfer the Cold War to a different and infinitely more dangerous locale.

Our intentions in Lebanon are honorable. The dilemma is how to bolster the new national government without turning it into an American client and the country itself into a Cold War battlefield. The solution is to insist that the world shoulder the burden of Lebanon--that like the troops already there, additional ones be drawn mostly from the international community.

At the moment, though, we are backing with both troops and money a government headed by a Christian in a majority Moslem land. For all the hosannas being shouted to unity, Gemayel remains the leader of a single Christian group and certainly not the darling of the Moslems. Lebanon has a tendency to shred, and when it does we may wind up backing nothing more than a sectarian leader and implementing a failed Israeli policy.

As tiresome as Vietnam analogies are, they are sometimes useful. With Lebanon, we face the danger of becoming embroiled in its internal disputes -- propping up a government that, like the ones we supported in Vietnam, simply may be unable to govern. More American troops are not the answer. They probably wouldn't solve Lebanon's problems, but they would certainly make them our own.