If a peaceful solution is found in Lebanon, a good part of the credit will go to Saudi Arabia, according to Arab sources here.
Working behind the scenes, the Saudis have helped to bring about the agreement in principle on certain issues which seem to have been reached in Lebanon between the Lebanese government and the Palestine Liberation Organization (PLO), Arab diplomats say.
In their usual discreet, and for the most part secretive, way, the Saudis have also been in frequent contact with United States officials. Some Western news reports have indicated that the Saudis have threatened to use their ''oil weapon'' against the United States in the event that Israel launched a full-scale attack on Beirut. But sources close to the Saudis say that this type of direct threat is not in keeping with the Saudi style.
Instead, the Saudis have warned the US that the humiliation of the PLO could cause a ''radicalization'' of the Palestinian leadership and of public opinion throughout the Arab world. This, in turn, they have warned, could threaten the stability of moderate Arab regimes. In order to show that there might be some teeth in Saudi warnings, the official Saudi Press Agency issued a Royal Palace statement on June 21. It said that an Israeli invasion of Beirut would result in the Arabs exercising their right of defense with ''all their potentials.''
The Saudis do not get much more specific than that. But while noting that an Arab oil embargo would likely be ineffective under current conditions, the Washington Report on Middle East Affairs, a publication of the American Educational Trust, says, ''There is no room for US complacency'' in this matter.
G. Henry M. Schuler, a former American oil company negotiator, says that while Saudi Arabia is unlikely to impose an embargo over Israel's move into Lebanon, the total humiliation of the PLO would more likely than not lead to Saudi oil policies which are less accommodating to the US.