Lebanon swirls in a welter of problems as the PLO fighters of west Beirut depart for other shores. Not least of them is how to get all foreign forces out of Lebanon - the Israelis, the Syrians, and the thousands of guerrillas still remaining in northern Lebanon. Amid all the uncertainties, however, US Secretary of State George Shultz is helpfully cutting through to the central issue: the urgent need to resolve the Palestinian question. By doing so, he gives hope that the United States will not let the tangle in Lebanon obscure or hold up early attention to this long-term objective.
Like any careful diplomat, Mr. Shultz would not let himself be drawn into a provocative statement about Palestinian self-determination when interviewed on NBC's ''Meet the Press'' over the weekend. That term, he said, has come to be a buzzword for a Palestinian state and therefore he declined to use it. But he left no doubt of his sympathy for the plight of the Palestinians, commenting that they should have ''some sense of diginity and control over their lives'' and ''a voice in determining the conditions under which they're governed.''
That may not be as strong a statement as some would like. Indeed it is a reflection of the difficult state of affairs that even so straightforward a term as self-determination has to be avoided. Mr. Shultz obviously does not want to prejudice a future negotiation by implying a solution before the parties even sit down together. Yet it will not be lost on the Palestinians that he reacted positively to an article in the Washington Post by President Mubarak of Egypt calling, first, for the US to recognize the right of the Palestianian people to self-determination.
It was especially important for the secretary to reaffirm publicly the US commitment to United Nations Resolutions 242 and 338, which call for Israeli withdrawal from occupied territories and which provide the framework for the Camp David autonomy talks. Doubts about the Reagan administration's stand are allayed by Mr. Shultz's statement that the US expects Israel to pull out of the West Bank and Gaza Strip - but behind adjusted frontiers assuring Israel's security.
It is too early to know how US policy in the Middle East will evolve. Secretary Shultz clearly is schooling himself in the region's problems. But already his quiet evenhandedness - displayed in his firm reiteration of US support for Israel and in his criticism of PLO as well as Israeli actions - and his focus on the fundamental imperative of Middle East peace are reassuring. They offer promise that American diplomacy is moving in constructive directions.