A stir has arisen over President Reagan's surprise statement that he won't permit the transfer of more F16 warplanes to Israel until Israeli forces leave Lebanon. But why should there be any fuss, on the American side at least?

The planes have been on hold since Israel invaded Lebanon last June: the administration has said it was studying whether Israel used them for other than the approved purpose of self-defense. Mr. Reagan simply updated the public rationale for the hold in order to apply a bit more pressure for the sake of Lebanon. You could say he has shelved the question of Israel's purpose last summer and decided instead to release the planes, as soon as Israel withdraws. From using the F16 question as a stick, he has turned to using it as a carrot.

The Israelis are unhappy. They contest any suggestion that their purpose in Lebanon last summer went beyond self-defense or that their purpose now goes beyond negotiating an early departure. They believe that their preferred role as a strategic partner, standing up these days to the newly reinforced Soviet client regime in Syria, should override any American reservations about their regional policy. And they resist any American use of arms supplies as stick or carrot, saying the practice (not unprecedented) is counterproductive.

There is something, of course, to all of these considerations, but not much. Surely no one would argue that the United States has no right to use its power to serve its policy. The practical consideration is to do it well. In the current circumstances, the announcement of a new explanation for withholding planes--planes that were already being withheld, that the Israelis were in no hurry to acquire before June and whose delivery was not scheduled to start for two more years --is a gesture, not a blow.

In their talks with the Lebanese the Israelis appear to be insisting still on the sort of continuing presence in Lebanon that would bring Israel some immediate comforts but would contribute to the further sapping of Beirut's authority--precisely the condition that has caused Israelis, not to speak of Lebanese, so much grief in the past.

Israel's agreement to withdraw is the expected key to parallel Syrian and PLO withdrawal and the eventual reconstitution of Lebanon. On the United States' capacity to bring off the removal of foreign forces rests in turn its ability to induce Jordan to sit down with Israel to negotiate peace. These are the stakes for American diplomacy in the Middle East. Unquestionably they are large enough to justify President Reagan's decision to put a small new weight on the scales.