Mr. Begin's decision to delay

Just as in the final stages of the 1973 war in the Middle East, more has been going on behind the scenes in this latest Arab-Israeli war than has appeared on the surface.

The clue to events in motion behind the scenes lies in the fact that Israel's armed forces had bottled up the Palestine Liberation Organization guerrilla army inside west Beirut by June 24 - the 18th day of the invasion, which began on June 6.

It may have taken the Israelis another two or three days to bring up their major assault weapons and men. But the Israelis were clearly in a position by the end of June to have launched the assault that presumably would have destroyed the last important part of the armed force of the PLO.

There can be little doubt about the preference of the two leading figures in the Israeli government, Prime Minister Menachem Begin and Defense Minister Ariel Sharon, for doing just that.

Why the delay over storming west Beirut?

Great pressure must have been brought to bear on Mr. Begin behind the scenes to cause him to hold back his battle leader, Mr. Sharon, for the second dramatic time in that warrior's career. In the 1973 war it was General Sharon who led the Israeli counterattack that surrounded the Egyptian III Corps of some 20,000 men and could, had he not been strenuously restrained, have captured it.

General Sharon was restrained in 1973 by pressure from Washington stimulated by Soviet preparations to send a major airborne force to Egypt.

Would the Soviets actually have sent that force to the rescue of Egypt's endangered III Corps? Washington did not know. But it did tell Israeli Prime Minister Golda Meir to rein back on General Sharon, which she did.

In this latest case Moscow has played a different game. There has been little hint of possible Soviet intervention with its own armed forces. But Moscow has used its propaganda apparatus at full speed to remind everyone that Israel's invasion of Lebanon was done primarily with American weapons and under the tacit diplomatic protection of Washington.

Any storming of west Beirut would be ugly. Casualties would be heavy on both sides. The world, vigorously assisted by Soviet propaganda, would inevitably place the ultimate blame on the United States for another human tragedy, since such an onslaught could be done only with weapons provided by Washington supposedly only for the ''defense'' of Israel.

By the time Mr. Sharon had his tanks and guns in position for the storming of west Beirut, world opinion had been shocked by the amount of death and destruction already caused during the invasion of Lebanon. And not only outside world opinion. One casualty of the invasion was the surface unity of the Jewish community in the US.

In its previous wars Israel had the support of the entire organized Jewish community in the US - the largest single Jewish community in the world. Individuals sometimes disapproved. Individuals sometimes spoke against Israel's policies privately.

But in public there was little if any serious breach on the surface of the community until the first week of July while the world watched and waited for the blow which Mr. Sharon had forged and which was ready to fall.

This time many leading members of the Jewish community did speak out in protest, calling for an end to the invasion before more damage had been done. They included two well-known and respected Jewish literary figures in the US, critic Irving Howe and Nobel laureate Saul Bellow, and such distinguished academics as Profs. Seymour Lipset of Stanford and Nathan Glazer of Harvard. The surface of American Jewish support for Begin policies had been broken.

Western Europe was obviously in action behind the scenes. France was known to be active. We can presume that London and Bonn were quietly urging Washington to apply the brakes on Messrs. Begin and Sharon. We do not know what word was sent privately from President Reagan to Mr. Begin. But the mere fact that Mr. Sharon's awesome blow was being held back was in itself evidence that the American President must have said something impressive.

Perhaps the acceptance of the resignation of Alexander Haig from the State Department also gave Mr. Begin some pause. His successor, George Shultz, is on the record as less committed than was Mr. Haig to the doctrine of Israel's military value to the US.

And, finally, the storming of west Beirut would mean Israeli casualties - perhaps more than during all the fighting on the way from Israel to Beirut. Israeli public opinion reacts adversely to Israeli casualties.

So the well-prepared blow was ready from the beginning of July. It had not been delivered as this was being written. Indications seemed to be that it would continue to be held back, although Mr. Sharon is a determined man and reportedly has resented the fact that he was not allowed to capture an Egyptian army in 1973.