The Airborne Warning and Control System strategy session involving the president's most senior advisers and the Senate's most junior Republicans came down, last week, to a central question: Is it possible to design a fig leaf that will be Government Printing Office issue, Grand Old Party origin and geopolitically substantial enough to let five reluctant Republican freshmen return in dignity to their president's side?

The answer, for at least some of those present, was probably not.

So the meeting last week in the office of Indiana's freshman Sen. Dan Quayle adjourned without assurance that this hurried trip to Capitol Hill by White House chief of staff James A. Baker III and White House congressional liaison Max L. Friedersdorf had produced any new converts for President Reagan's anxious AWACS fold.

Converts are the key to the Selling of the AWACS, latest in Reagan's salesmanship series. But the White House campaign for Senate approval of its planned sale of five sophisticated intelligence-gathering planes to Saudi Arabia has produced more action than momentum.

In this latest battle of Capitol Hill, White House strategists began maneuvers last week aimed, in one's words, at "capturing the top of the news." Under the marshaling of Baker and Friedersdorf, senators favorably disposed to vote for the AWACS in the first place were brought in, one by one, for brief chats with Reagan and lengthier statements of support to the press.

But capturing the top of the news does not necessarily make one King of the Hill. And with just about one week to go before the crucial Senate vote, the president's strategists had to face the mathematical facts of life: Of the 50 original signers of a resolution by Sen. Bob Packwood (R-Ore.) opposing the AWACS sale, only two have had their minds changed by the president. Forty-eight remain firmly opposed.

Among those still opposed are Robert W. Kasten Jr. of Wisconsin and Slade Gorton of Washington. They were in that meeting last week in which the senior presidential advisers sought to help five Republican freshmen draft a compromise that would permit them to vote with the president for the AWACS sale.

The drafters' problems are a good indication of those the president faces in trying to avoid what could be an internationally embarrassing defeat.

White House strategists had viewed the meeting basically as a way of helping these freshmen find a compromise that would be marked with their own identity.

But at last week's meeting, Kasten told the president's advisers: "In order for me to reverse my position there has to be a substantive change." Either the Saudis must be willing to join the Mideast peace process as outlined in the Camp David accords, he said, or there must be a significant change in the American participation in the command and control arrangements for the planes. The Reagan administration had agreed to allow the Saudis to have eventual command and control of the planes they are purchasing.

Baker was said to have responded to the first point by noting, as the president has in virtually every meeting he has had on the subject, that the Saudis had helped significantly in the quiet diplomacy that resolved the latest crisis in Lebanon. But the Saudis cannot embrace the Camp David accords because of their own internal political problems.

To Kasten's second point, Baker said flatly that he did not expect any further movement on the crucial command and control question.

Kasten left the meeting saying he had not been moved. Gorton left telling aides his position was similarly unchanged. And the president's advisers left knowing the enormity of the job that lies ahead.

For all the talk of momentum and movement, for all the effort to parlay Anwar Sadat's assassination in Cairo into an AWACS victory in the Congress, the basic arithmetic, as one White House senior strategist explained it, is still this:

"Packwood still has 48 names . . . and he may have five others in addition to that. We may get three or four of those."

By this White House count, the anti-AWACS forces could have a majority of 53 votes in the 100-member Senate, with the president's fortunes resting on converting enough to produce perhaps a tie, or perhaps a one-vote victory.

"That," said the Reagan strategist, "is what we mean when we say it is winnable."

EPILOGUE: They were the men who brought you the last 20 years. Sixteen former secretaries of defense and state and advisers on national security, together now as salesmen in the campaign to help Ronald Reagan send AWACS to Saudi Arabia. They posed for pictures under the North Portico of the White House, and their joint statement was read to the press. Then one senior official who served a past Republican president strolled to the side and considered how the current AWACS crisis had come to be.

"The sale should go through--it's in our national interest," he said. "But they sure have messed this up. It was poorly negotiated in the first place with the Saudis . . . . And now the Saudis are being asked to lose face publicly or be slapped in the face with a defeat in Congress. It was sloppy, just sloppy."

Last April 1, as President Reagan lay in his hospital bed two days after the attempt on his life, the AWACS sale was steered through a National Security Council meeting. Defense Secretary Caspar W. Weinberger was at the controls. Secretary of State Alexander M. Haig Jr. and national security affairs adviser Richard V. Allen opposed including AWACS in the military package for Saudi Arabia, saying it would be difficult to win congressional approval.

No more than 35 senators will oppose the sale, Weinberger said. In a crucial miscalculation, according to a senior administration official, the National Security Council did not debate whether AWACS should be offered to the Saudis on the same terms under which it is flown by the North Atlantic Treaty Organization allies--with a joint command and control agreement.

Haig, who had weakened himself internally in unnecessary rounds of turf fights, was overridden, and negotiations with the Saudis were handled by Weinberger and Defense. The idea of a NATO-like joint command and control structure was never pressed and negotiated with the Saudis, this official said.

"No one in that National Security Council meeting even thought of it," a senior Reagan adviser said. "Had that been done at the time, it would have made our job a lot easier now."