Washington — At first glance, it has looked easy: cut off American aid to Israel, and the Israelis will hold their fire. Then, supposedly, the negotiations for the evacuation of the PLO could succeed.
But in fact it has never been that easy. A cutoff of American military or economic aid to Israel would not immediately slow Israel's war machine, according to Reagan administration defense experts.
Israeli officials agree with this assessment. Indeed, they argue that such a cutoff might cause Israel to take even less account of American requests for restraint and to hit even harder at the Palestine Liberation Organization (PLO).
Israel is now considerably more self-reliant in the type of munitions which it has been expending in and around Beirut than it was when it fought the Yom Kippur war of 1973. At that time, Israel was so short of supplies that it required a major American airlift within days. Under Egyptian and Syrian attack, it was losing dozens of warplanes and hundreds of tanks.
After the 1973 war, the Israelis vowed ''never again,'' and intensified their efforts to produce their own war materials. In the current fighting, Israel's losses of tanks and airplanes have been minimal. And many of the shells and missiles that are being fired by the Israelis have been produced not by the US but by Israel itself.
One American analyst estimated that if the Israelis had to continue to fight at the same level of intensity with which they fought in Lebanon in recent weeks , they could continue without any real strain, or without American resupply, for 30 days or longer. For this they could rely on their own stockpiles.
The Reagan administration has stopped just short of threatening sanctions, in part apparently because it believes that there is no easy answer to restraining Israel and in part, apparently, because President Reagan himself is reluctant to take the advice of top officials who have been pressing for a harder line against Israel.
William B. Quandt and Harold Saunders, two former high-ranking officials who were involved in Carter administration attempts to restrain Israel, are convinced that given the Reagan administration's past leniency in dealing with Israel, any threat of a US aid cutoff would at this point lack credibility. At the outset of the Israeli invasion of Lebanon two months ago, the Reagan administration gave, if not a green light, at least a yellow light to the invasion, they say. And, as Israeli officials point out, President Reagan himself has repeatedly acknowledged that the US shares Israel's stated objective in Lebanon: the expulsion of all foreign forces from that country, including, first and foremost, the PLO.
Israeli officials, for their part, seem to be persuaded that in the end Reagan administration officials, regardless of whatever anguish they may suffer over civilian casualties, will welcome what Israel is doing in Lebanon as in the American interest. As the Israelis see it, the Reagan administration wants to share in the benefits of what they are doing without suffering from any of the moral outrage which Israel's attacks have triggered around the world.
''We're getting the clear impression that everyone understands it would be better to finish the job by military means, but they want us to do the job and to let us take the blame,'' one Israeli official told this reporter recently.
''Sanctions against Israel would be counterproductive in several respects,'' the official continued. ''It would give away the threat which the US needs to get concessions from the PLO. And it would mean that in the future, Israel would not owe the US even the minimal obligation any more.''
The Israelis further argue that they have been doing the US a favor in Lebanon in part because they have demonstrated the superiority of American weapons over the Soviet arms which have been used by Syria and the PLO. To weaken Israel through sanctions would be to weaken America's only reliable ally in the Middle East, Israeli officials say.
That has long been the view of none other than Ronald Reagan. But the President was angered when the Israelis ignored his calls for restraint around Beruit. In his view, Israel's continued military action endangered negotiations aimed at securing the PLO's departure.
Should the President decide at some point to impose sanctions against Israel, there is little doubt the long-term impact might be profound. For the short term , the effect would be mostly psychological and political. But in the long term, Israel's heavy dependence on American economic and military aid would begin to show.
Washington gives Israel more in economic and military support than it provides to any other country in the world. With less than a 10th of 1 percent of the world's population, Israel receives nearly a quarter of America's overseas aid.