Several Israelis have proposed an international military force to police southern Lebanon that might include American troops. And the United States is not ruling out the idea.
''It's too early to say,'' said US Secretary of State Alexander M. Haig Jr., when asked about the proposal in Bonn. His little-reported remarks caused a minor stir in Washington.
''It would depend fundamentally upon the mission, the composition of the force, the political mandate under which such an American contribution might evolve,'' Mr. Haig said. ''It isn't something we're leaning heavily in the direction of at all.''
While obviously not the administration's top priority at the moment, the idea that American troops for southern Lebanon would be considered at all is viewed as significant by some here.
Patching such a force together would be an exceedingly difficult task, both because of the risks involved and possible Arab opposition to such a force. And domestic opposition - not least from Congress - would make American participation unlikely. Many senators and congressmen have their doubts about dispatching American soldiers to participate in the recently formed international peacekeeping force for the Sinai, an assignment that entails fewer risks than duty in Lebanon.
''I can't imagine it, frankly,'' says Dean Brown, a former US special envoy to Lebanon and president of the Middle East Institute here, in reference to American participation in an international military force in Lebanon. ''It isn't the Sinai desert, where you have peace between Israel and Egypt.''
''American troops in southern Lebanon would eventually take casualties from one source or another,'' the former ambassador says. ''After Americans take a close look at this, I doubt that many of them would be enthusiastic.''
Shimon Peres, the Israeli opposition leader, said in an interview with the ABC television network that the timing of an eventual Israeli withdrawal from Lebanon would ''depend very much upon the international force that is supposed to replace the Israeli forces.''
An Israeli embassy official says an international peacekeeping force for Lebanon is only one of the ideas under consideration at the moment.
''It depends on Lebanon itself and the Lebanese people,'' the official said. ''We know what we would like to achieve, but we have no idea yet how this arrangement will be worked out.''
Congress, meanwhile, has not yet debated proposals for a peacekeeping force. Events in Lebanon have moved so rapidly that it has been difficult for anyone in the Congress to know what was going to happen next. And many congressmen have been devoting nearly all of their time to budget decisions.
But several congressmen of Lebanese descent have been circulating a resolution that calls for a cease-fire, the withdrawal of Israeli troops, and the withholding of American aid funds until a withdrawal takes place.
Rep. Clement J. Zablocki (D) of Wisconsin, chairman of the House Foreign Affairs Committee, has been looking into the question of the legality of the Israelis' use of American weapons in Lebanon. The Israelis argue that they have been using those weapons strictly for defensive purposes, as required by US law.
Representative Zablocki says that support for Israel here has ''somewhat diminished'' in the wake of the Israeli invasion of Lebanon.
''There's less support for Israel than . . . in the past,'' he said. ''Now they've gone after the Syrian missile sites, and they seem to have gone beyond just going after the Palestinians.''
Israeli officials contend that Syria opened fire with its missiles on Israeli fighter planes, thus provoking the Israeli attacks on Syrian antiaircraft sites.
One congressional staff specialist on the Middle East says that aside from Mr. Zablocki's comments, reaction by members of Congress to the Lebanon invasion has so far been restrained.
''They are concerned about a possible expansion of the war to include Syria and the Soviet Union,'' the staff aide said. ''But their reaction has been very muted.''