THE UNITED STATES has lofted a curiously airy proposal to break the deadlock over Lebanon caused by Syria's intransigence. It suggests that Israel draw up a timetable for its full withdrawal from Lebanon. The Israelis, it seems, are not actually being asked to withdraw unilaterally, which they have said and the United States has agreed they will not do. The idea is that the drawing up of a timetable might stir or shame Syria into drawing up a timetable of its own.

There is a kernel of legitimate foresight in this suggestion. The Israelis, pressed to near the bursting point by the casualties their forces are still taking in Lebanon, are contemplating a unilateral "redeployment" to a line meant to make the occupation less costly. Prudent people must fear that a cheap occupation might encourage the Israelis to settle in indefinitely. This would leave Lebanon even closer than it is today to being effectively partitioned. A timetable would be a device working to make "redeployment" temporary.

Otherwise, however, the proposal seems mostly to reflect the general frustration felt toward a Syrian regime that has broken its promise to its fellow Arabs to make a follow-on agreement to leave Lebanon, that ignores a unanimous vote by Lebanon's parliament in support of the agreement with Israel, and that now simply refuses to receive Philip Habib, Mr. Reagan's special envoy. President Hafez Assad is one disagreeable fellow. The more he gives over the defense of his country to a foreign power--the Soviet Union now has thousands of troops in Syria manning weapons and advising Syrians--the more he seems compelled to demonstrate his defiance and national pride.

The temptation for the United States is to tell the Syrians to go hang. But this, though deeply gratifying, would be shortsighted. Secretary of State Shultz, who is now intending to go on from South Asia to the Middle East, has reason to drop by Syria. The purpose would be to see for himself whether the Assad government is truly lost to posturing for the foreseeable future or whether it is open to an exchange. These are far from the best of circumstances for an American initiative whose results are problematical. But the plight of Lebanon, which stands to be divided even more deeply if the momentum of occupation is not slowed, calls out for some political risk-taking by Washington.