While President Reagan was lying in his hospital bed seven blocks away, the National Security Council, in secret session April 1, learned that his whole Middle East policy may founder on the U.S. Saudi arms deal.

The nation's top policy-making officials for the first time were given an informal Senator Jacob Javits at the request of the White House. It points to major defections sufficient to kill of arms deal if a vote were held today. The reason: Too many senators agree with Israel that Saudi Arabia is not giving enough in return for AWACS radar aircraft.

That raises this question: If Israeli opposition is viewed by other Mideast nations as strong enough in the U.S. Senate to overcome Ronald Reagan's first initiative in their Region, what will happen to U.S. influence in the Arab world?

The Israeli government two months ago instructed its embassy here not to attack Reagan's plan to supply fuel tanks and missiles for the Saudi F15s. Prime Minister Menachem Begin feared a bloody battle with the new, strongly pro-Israel president. But Reagan's decision to add the AWACS to the package changed Israel's mind, and the world from Jerusalem now is: Whatever the cost, stop Reagan's AWACS deal!

Helping that determination are the terms governing the AWACS sale, more favorable than the terms given West Germany several years ago. At the april 1 NSC meeting, Secretary of State Alexander Haig pointed this out and indicated the will try to win Saudi concessions when he goes to Riyadh on his current Mideast trip.

Haig repeatedly emphasized during the discussion that to get the deal through the Senate, critics would have to be persuaded that the United States was getting its full money's worth from Saudi Arabia.

Countering Haig, Defense Secretary Caspar Weinberger argued that the Saudis have agreed in a formal memorandum to a "regional" defense concept for the first time in the history of that highly nationalistic, isolationist kingdom. That alone is a big concession, he said, suggesting that other cooperative defense moves may be possible in the U.S. Sadui future.

But Haig asked whether the "regional" defense argument would be enough to persuade Congress. However valid that argument is in terms of Reagan's decision to foil Soviet intrusion into the Persian Gulf area, it may prove fatally flawed in terms of congressional politics.

Republican senators normally loyal to their new president have been getting signals from Israel that the Saudi deal will threaten Israel's military superiority in the Middle East. These senators protest that the AWACS are being sold to Saudi Arabia without any real quid proquo.

That explains Weinberger's heavy emphasis on Saudi willingness to concede that its security is part of a "regional," anti-Soviet problem. But opponents of the deal, led by the pro-Israeli lobby, want much more: a guarantee that in exchange for the Swacs the United States will get military facilities or base rights in the Saudi homeland. That's however, is regarded as out of the question by administration officials.

The opponents also argue that West Germany and other NATO states that have been sold SWACS automatically share with the United States all data picked up by these radar ships. No such arrangement has yet been negotiated with the Saudi government.

But the heart of Israel's objection has nothing to do with concessions to the United States. It is the fear the Saudis could use their AWACS to monitor Israeli military actions or even to vector (set the course of) Syrian or other Arab aircraft on anti-Israel missions.

In the hospital, Reagan has not begun to concentrate on remedies to save his Saudi deal and the strategic plan for building power in the Persian Gulf it is supposed to preface. But he has almost three months before Congress will vote. That is time enough to avoid a defeat that would begin his administration with a show of weakness profoundly disturbing to U.S. Arab relations.