Syria's President Hafez Assad once again seems to dominate in the Lebanon crisis. There appears to be little that the United States can do about that fact - with or without the US Marines.
But while a number of experts here have reached this conclusion, the Reagan administration is not admitting defeat. American envoys in Beirut and in Damascus are working around the clock to try to encourage a cease-fire and the formation of a new Lebanese government.
Israel, meanwhile, is urging the administration to do much more than that. Senior Israeli officials are reported to have advised the administration that no progress will be made toward a political reconciliation as long as the United States fails to make a military show of force in Lebanon. The officials have apparently recommended that the US consider using its ships to shell Druze and Shiite Muslim forces in the Beirut area.
In the Israeli view, the Syrians, who are the all important supporters of these Muslim forces, will not agree to a compromise settlement in Lebanon unless the balance of forces shifts against them. The Israelis have long been skeptical of American claims that the US-trained-and-supported Lebanese Army is becoming an effective force.
For the Reagan administration, the most frustrating factor is the apparent lack of any US leverage over the Syrians. The situation began to deteriorate last year after the Israelis withdrew from the Shouf mountains overlooking Beirut. The Israelis clearly would like to find a way out of Lebanon. The Syrians only have to read the Israeli newspapers to know this, and that is another reason why the Syrians now seem to dominate the situation.
Secretary of State George Shultz, in the course of a visit to Brazil, accused US congressmen calling for a withdrawal of the American Marines from Lebanon of contributing to Syrian intransigence.
Mr. Shultz said he thought Congress had decided the issue when it voted last October to let the Marines remain in Lebanon for 18 months. ''We should stand by that position and not give the image of here today, gone tomorrow,'' he said.
State Department officials say that the resignation of Lebanon's Prime Minister Shafik Wazzan now makes it necessary for President Amin Gemayel to form a new government that would include representatives from opposition factions.
But some experts agree with the Israelis that unless the Americans combine the use of force with the use of diplomacy in Lebanon, the Syrians will continue to undermine the Lebanese government and reconciliation process. Secretary Shultz said Syria had made ''direct threats'' against Muslim members of the Lebanese Cabinet, thus forcing them to resign.
But State Department officials insisted that despite the outbreak of fighting in Beirut, the Lebanese Army is holding together.
Officials said that Nabih Berri, the Shiite leader of the Amal militia, had called on Shiites in the Lebanese Army not to fire on their fellow Muslims. But the officials say that Mr. Berri did not go so far as to call on Shiites to leave their Army posts.
President Reagan stated on one occasion last year that if the government collapsed in Lebanon, the US might have to consider withdrawing the Marines.
The President later hardened his position, however. He stated in an interview with the Wall Street Journal that the withdrawal of the Marines would ''mean the end of Lebanon'' and the end of chances for an overall Middle East peace.
White House deputy press secretary Larry Speakes said Monday that the crisis in Lebanon may prove to be an ''opportunity'' to form a ''responsible, broadly representative government.''
Mr. Speakes said US envoys in the region, including President Reagan's special envoy, Donald Rumsfeld, have been actively involved in discussions with Lebanese leaders over the past two days.
State Department officials said that much might also depend on talks to be conducted in Damascus by Robert Paganelli, the US ambassador to Syria.