A year after the Israeli invasion of Lebanon, Menachem Begin seems to have won the larger of his two grand objectives and left most of those who do not accept his vision of the future of the area in a funk.

He has not accomplished his lesser, up- front objective, the one on which the operation was at first sold to the Israeli and world publics, of saving Israeli lives. An American-arranged Israeli-PLO cease- fire, applying to acts across the Lebanese border, had been in effect for almost a year before the invasion, totally halting Israeli casualties.

In and since the invasion, however, nearly 500 Israeli lives have been lost. This count, which is still running, is the principal source of the morose argument over Lebanon that Israelis are conducting among themselves.

Begin's larger objective was plainly to destroy the PLO as a political force in order to reduce the obstacles to continued Israeli absorption and eventual annexation of the West Bank. In this effort, his prime advantage was his and Ariel Sharon's clear sense of where they wanted to go; against Arab indiscipline and American innocence, it was no contest.

Begin has also had the generous if unintended cooperation of the PLO, which has done all he might have asked to render itself unfit as a political instrument: avoiding the hard facts of its situation, vetoing negotiations and now yielding to sometimes-violent internal warfare.

The result is an increasing tendency to bitterness, anti-politics and escapist apocalyptic thinking on the part of the Palestinians and their supporters. The most striking evidence of this tendency is a mental leap forward to a time when a terrible nuclear retribution will be exacted against the sinning Israelis.

Meanwhile, those who deplore Israel's policy, while caring for Israel, are reduced pretty much to enumerating the many real ways in which the country's better nature and potential are being warped in order to perform the distasteful and corrupting task of keeping a restive Palestinian population down. Those of us who had hoped that within the Israeli political society there was still the will to reverse the Begin policy, in order to deter this sort of damage and to improve the prospect for peace, have been forced increasingly on the defensive.

In the United States, a good number of people, in and out of the government, say grimly that the Reagan administration should keep moving ahead with its diplomacy in and over Lebanon, and with its plan of last Sept. 1 for Israeli-Jordanian-Palestinian talks. American self-respect as well as American self-interest is invoked to justify this course. But there is little confidence that such an effort will do anything more soon than expose the futility of American diplomacy, at least as far as the disposition of the West Bank goes.

Everyone has a clear idea--often a different idea--of the mistakes that were made in the past, but no one has put forth a clear idea of what might be done now, and what is do- able now, at least to prevent the situation from deteriorating further. By further deterioration, I mean not simply some kind of Israeli-Syrian clash and a deepening of the effective partition of Lebanon but also the process of Israeli colonization on the West Bank.

What complicates the situation is that anything that is conceivably do-able--and why talk about anything else?--is bound to play somewhat into Israel's hands, since its position of strength is a dominant fact. It offends the sense of fairness of many Arabs and even of some American officials that the Israelis should profit from things they should not have done in the first place. They regret that the requirements of diplomacy in Lebanon and politics in the United States have all but removed the earlier possibility of the United States' applying sanctions against Israel in order to enforce the president's call for a West Bank settlement freeze.

Nonetheless, in the circumstances there is no ready or responsible alternative to plodding along in Lebanon, the one place where, in respect to Syria, there is still a glint of gray in the black otherwise to be seen at the end of the tunnel.

If the Palestinians cannot be kept from extending their own dispersion and misery, and if the Israelis cannot be kept from devaluing and pauperizing their country, then perhaps something can still be done for Lebanon. It would be worth concentrating on this effort even if there were an early prospect of doing something more.