Since Lebanon's independence in 1943, its dream has been a carefully balanced coalition held together by a presumption of equal treatment for all religious communities. The fragile network of understanding has been shattered in the past, then patched up, and then shattered again.

Unfortunately, it is again on the path to disintegration. In 1958, American Marines and an astute political operator, the late ambassador Robert Murphy, were able to facilitate the patching process. Today, American Marines may be watching, or even participating in, a collapse.

What has happened? Malik Salam, a respected Moslem leader, says the Lebanese parliament elected Amin Gemayel as president of Lebanon, but it did not elect the Maronite Phalangist party and its private militia to take over power in the country.

Walid Jumblatt, leader of the Druze, believes there was a political deal with the Phalange before the Lebanese army went into Christian East Beirut, the Phalange's home territory, earlier this year. He insists he will not let that army into the mountainous Chouf area--where Druze have lived for centuries-- until there is a far-reaching political understanding with the central government.

The type of understanding he--and many Sunni and Shia Moslem leaders--seek is not clear; little is clear in Lebanon. It increasingly appears to be a demand for change in the political structure of the country that would permit a greater sharing of power. "Greater sharing" could lead to a denunciation of the decades-old unwritten National Covenant, which gives the powerful presidency, army command and parliamentary control to Maronites, or it could be the creation of a government of reconciliation to include leaders like Saeb Salaam, a respected Sunni, Nabih Berri of Amal, which is the Shia fighting force, and Druze leader Jumblatt.

In a powerful end-of-Ramadan address this summer, the leading Sunni religious figure, addressing tens of thousands of Moslems in the Sports Arena, said there can be no usurpation of power by one armed group, that political power must be shared through a revision of the National Covenant and that all private militias--not just some --have to be disbanded.

It is this last point that has precipitated the present crisis. On Aug. 16 Israeli Defense Minister Moshe Arens flew to Beirut where he met, first, with Sheik Pierre Gemayel, head of the Phalange political party and, second, with Fadi Frem, the commander of the Phalange militia. The minister said later he had urged "political accommodation between the Christian and Druze communities."

In Beirut, however, the meeting was viewed differently. Non-Maronite Christians and Moslems alike saw it as a blessing of the Phalange forces. It exacerbated their fear that Amin Gemayel was not a president committed to protect all religious communities but the captive of the Phalange militia that had already flexed its muscles in Beirut, the Chouf and the south.

From fighting over turf in the Chouf between Maronite and Druze forces the conflict has spread to Beirut, involving not just Druze and their new enemy, the Lebanese army, but others. The Shia militia, Amal, is heavily armed and is driven by the demand for "social justice" that we saw in the struggle against the shah in Iran. It has entered the fray. So have the long-dormant Murabitoun, a leftist and originally pro-Nasser force.

Fighting now is as complicated and as difficult to understand as it was in 1976. The chief difference is that the PLO is not involved and that the multinational force can become the accidental--or perhaps, if fighting rages uncontrolled--the planned target. We are not yet at the latter stage. Much of the fighting is a form of political bargaining. The Druze and Moslem groups are saying: "We too have arms and power. If you refused to hear our pleas in former times of peace, we'll make them louder today with guns." This sort of political bargaining can quickly degenerate into chaos.

This is where the United States comes in. Washington talks of sending in more troops or pulling them out. But it's not that simple. It is obvious that the nature of the game has changed. From unloaded rifles when they arrived a year ago, the Marines have moved to exchanging fire--often with unknown opponents. The hope that the presence of a multinational force would calm the situation and then lead to popular support of a strong central government whose army would control and disarm the multiple militias is gone. Instead, American, French, Italian and British troops are close to being regarded as allies of a central government under Phalange domination. This is a dangerous situation.

It was indeed former Israeli defense minister Ariel Sharon's desire to see a Maronite- dominated government in power, a government that could sign a peace treaty with Israel even if it meant cutting off Lebanon from the Arab world. Many Lebanese Moslems, who saw themselves no longer as unequal partners in a national consensus but as doomed to subservience in a one-party state, viewed American policy as supporting the Sharon line. Constant American repetition of a policy toward Lebanon of territorial integrity, independence and creation of a strong central government--without ever a word about political reforms or the need to recreate a national consensus based on power sharing --amplified the fears.

American policy toward Lebanon needs a dramatic change. It cannot rely on the premise that the Soviet Union and Syria are somehow behind all the troubles, that Syrian and Israeli withdrawal will somehow bring peace or that a Phalange-dominated government can prevent a renewed outbreak of guerrilla and urban warfare.

Instead of relying solely on President Gemayel, the UniteddStates should turn its energies toward the creation of a new national consensus. Once again--how often does it have to be said?--the United States needs to support widely shared aspirations rather than personalities.

In June 1982 Henry Kissinger wrote in The Post that the Israeli invasion of Lebanon "opens up extraordinary opportunities for dynamic American diplomacy in the Middle East." How pretentious that all seems today. How necessary it is to deal with the perverse realities.