According to Secretary of State George P. Shultz, there are a number of reasons the United States went wrong in Lebanon - none of which seem to relate to actions of the Reagan administration.
As Mr. Shultz has explained it in interviews and congressional testimony, debate in the US Congress over America's Lebanon involvement ''took the rug out'' from under the US diplomatic effort. Shultz has pointed to Syrian intransigence as a key factor in the Lebanon setback.
He has also expressed disappointment in the Lebanese parties to the conflict and their failure to achieve a reconciliation. And in some quarters of the State Department, there is disappointment that Saudi Arabia did not practice more effective diplomacy and that Israel did not play a more active role in bringing pressure to bear on Syria.
But there seems to be little questioning at the top level at the State Department as to whether the administration itself might have miscalculated in Lebanon.
''You're not getting an intelligent assessment of lessons learned here,'' said a department official who has in private conversations criticized for some time the approach of top-level officials to Lebanon. ''You're getting sour grapes.''
''We never understood that we didn't have the assets to carry out the macho policy we were launched on,'' he said.
''There was an assumption in the administration that just about anyone can handle foreign policy,'' the official continued, implying that this assumption still holds. The most experienced Middle East experts in the career Foreign Service were the least consulted in recent months by Secretary Shultz and other top-level officials, he stated.
Outside the government, there is a widespread belief among diplomats and scholars that the administration stumbled badly in Lebanon.
The lessons to be learned, they say, concern the limits of force, the use and misuse of special envoys, and the need to define more precisely American interests and objectives.
In an interview with the Wall Street Journal last week, Shultz appeared concerned that the US experience in Lebanon will reinforce a perception that America, almost a decade after the fall of Saigon, still has difficulty using military power successfully.
Many of his critics would agree with Shultz in arguing that Lebanon was not a real test of American military power. But they contend the administration went astray when it began to multiply its aims beyond the original role of the Marines.
* Lesson No. 1, say the critics, is that if you are going to send peacekeeping forces, set realistic goals, and stick to them. Don't get diverted beyond your means.
* Lesson No. 2: Don't get involved in backing one side if you want to be seen as an honest broker with all sides.
As one expert with long experience in organizing such peacekeeping forces explains it, the American Marine contingent - limited though it was in size - became a major psychological prop for the Amin Gemayel government. At one point, President Gemayel seemed to think that the Americans would solve all his problems, leaving him in a position to resist making concessions to his opponents.
At the United Nations, Brian Urquhart, undersecretary-general for special political affairs, has argued that a peacekeeping force ''must use force only as the last resort of self-defense.'' But the US members of the multinational peacekeeping force in Lebanon, who entered Lebanon originally to oversee the evacuation of Beirut, were in the end perceived as using force in support of the Gemayel government and against Syria.
As Daniel Pipes, a historian and student of Islam, saw it, the United States ended up trying to pursue two mutually exclusive goals. One was to bring peace to Lebanon, and the other was to ensure a pro-Western government.
According to the Pipes thesis, the latter policy implied Maronite Christian political domination and a preservation of the inequalities that provoked Muslim discontent and led to civil war in 1975.
William B. Quandt of the Brookings Institution, former Middle East director of the National Security Council staff under President Carter, sees a future Lebanon that will be ''less overtly pro-US, less overtly pro-Israel and more attentive to Syrian concerns.''
According to Dr. Quandt, Syria is not in a position to dominate all of Lebanon. It is likely, however, to be the leading influence in the northern and eastern parts. Israel retains a hold over the south.
* Another lesson: Don't underestimate the power of Syria to work against US interests, and don't overestimate the ability of Israel to work in favor of those interests. Administration officials believed that with Israeli artillery in range of Damascus, the Syrians would avoid confrontation in Lebanon and accept a Lebanese-Israeli withdrawal agreement that gave substantial Israeli concessions.
''We underestimated the Syrians,'' Quandtsaid. ''We acted as if they had been decisively defeated in 1982. They were wounded but not defeated.''
Quandt said the US also overestimated the ability of Saudi Arabia to influence the Syrians.
The administration further miscalculated, Quandt argues, in its use of special envoys such as current envoy Donald H. Rumsfeld. He said that beginning with the shuttles of former Secretary of State Henry Kissinger, Middle East leaders grew accustomed to making concessions only if they were dealing directly with the President or secretary of state.
Syrian President Hafez Assad never lets anyone forget that Dr. Kissinger flew as many as 30 times to Damascus before sealing the 1974 disengagement deal.
Secretary Shultz has met with Assad. But State Department officials concede that he may have been late in making his first trip to the region in 1983.
Few critics seem to think there are sure-fire solutions to Lebanon's complex problems. President Reagan saw Lebanon as an arena for US-Soviet competition. It turns out to be a nation, the critics say, that defies such simplification.
Brent Scowcroft, national-security adviser to President Ford, asserted recently that if the administration had moved swiftly in the fall of 1982, when the situation was still fluid, it might have been able to bring about a settlement more to its liking. But General Scowcroft also said, ''There are certain problems that don't necessarily have any good solutions. I know it's un-American to say that. But Lebanon may be one of those problems.''