Washington — 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.
In pursuing their goals, says Mr. Schuler in a recent paper on ''Petropolitics,'' the Saudis ''have only one significant instrument - oil policy.''
Mr. Schuler's prediction as to Saudi policy over the long run is: ''restraining production so as to allow a steady rise in real oil prices.''
Clovid Maksoud, the chief representative of the 21-nation Arab League in the United States, declines to speculate about Saudi oil policy. But in an address to a seminar at the Center for Strategic and International Studies of Georgetown University on June 30, Mr. Maksoud predicted that as a result of the Israeli invasion of Lebanon, moderate Arab states will ''distance themselves'' from the United States. Such distancing, he said in an interview, might consist of a downgrading of diplomatic relations and of the ''reduction of economic ties.''
Ambassador Maksoud says that ''disinformation'' circulating in Washington to the effect that the Saudis are secretly pleased to see the PLO suffer a defeat is totally false.
''But the more it becomes advertised that they would like to see the humiliation of the Palestinians, the more they will reassert their commitment to the PLO,'' said Ambassador Maksoud. ''They might be pushed to go beyond what they actually want to do.''
Mr. Maksoud said that one consequence of the Israeli move into Lebanon which has already occurred is a ''convergence of positions'' on Lebanon between Saudi Arabia and Egypt. He said that Egypt was likely to significantlytone down negotiations with Israel within the Camp David framework.
Meanwhile, the smaller Gulf states are also letting Washington know of their concern over the possible consequences of the invasion. The foreign minister of Bahrain, on a visit last week, urged US officials to reassess American policy in the region and take steps to help assure genuine self-determination for the Palestinians.