President Reagan has worked his will with Congress once again and this time at a particularly crucial moment in his presidency. By winning - even narrowly - approval for the sale of airborne warning and control system (AWACS) aircraft to Saudi Arabia, he has sent a strong signal to the public and Congress that he is still very much in command.
The signal was needed. The public was beginning to view the President as faltering a bit after his impressive start. The economy was sagging. Congress was becoming less cooperative. There were signs that Mr. Reagan was beginning to lose his ability to control events.
But now with last-minute persuasion and political arm-twisting, the President has won another ''big one.'' Once again he has shown his mastery over Congress, this time overcoming the efforts of the powerful pro-Israel lobby. And he has won a victory which he says is vital to maintaining peace in the Mideast.
More than anything else, the President had made the $8.5 billion arms package , which includes the controversial AWACS planes, a test of his standing in the world and of his ability to conduct US foreign policy. Foreign policy experts say that a Reagan loss on this issue perhaps would have dimmed his influence abroad, but not by much and not for long.
The political aspects of Reagan's AWACS triumph include:
* Reagan's people had been slow to enter the contest for Senate support. Thus , they had to overcome an extremely large lead. Very early, Sen. Alan Cranston (D) of California, the Senate minority whip, had a list of ''committed'' Senate opponents numbering 50. On top of that there were a number of uncommitted senators, many of whom seemed to be leaning away from the President on this issue.
But the President, with another show of his skill at personal persuasion, worked hour after hour and day after day in the last couple of weeks to turn the tide. The surprising turnabout of Sen. Roger W. Jepsen (R) of Iowa reflected how formidable Reagan is when applying his brand of charm and smilingly applied pressure.
Through an 11th-hour letter to Senate majority leader Howard H. Baker Jr. (R) of Tennessee on Wednesday, Reagan told the Senate that the Saudis had agreed to conditions for the security of the AWACS that include continual US on-site inspection and surveillance. He wrote that the conditions ''go well beyond'' Saudi Arabia's firm commitment to abide by the normal restraints that are part of US arms sales. He said the planes will be transferred to Saudi Arabia only after the President certifies to Congress that the security conditions have been met.
* Veteran presidential watchers here are saying Reagan's victory was more symbolic than substantive. They believe that had he not made so much of the sale it would not have been so important that he prevail. But more than that they are underscoring that the presidency was beginning to look a bit adrift - and that this come-from-behind victory helps Reagan regain the momentum he needs to carry forward with the new initiatives he is bringing to Congress.
* Finally, there is the political status of Reagan after the struggle. Rep. Guy Vander Jagt (R) of Michigan says: ''Such a stunning victory adds to his luster, glitter, glamour. It adds to his leadership ability. And it helps him enormously with Congress.''
Reagan Chief of Staff James Baker III had said before the vote that while he expected to win on AWACS, ''this might be our first defeat.'' He said Reagan was prepared to lose a ''big one'' at some point.
From a military standpoint, Pentagon officials say the President's victory gives Saudi Arabia a far greater ability to protect its critically important oil fields, which provide 25 percent of US oil imports. With the radar surveillance AWACS provides, the Royal Saudi Air Force will have enough time to scramble its fighters and intercept attacking aircraft before they reach Saudi oil fields, say Pentagon officials.
Moreover the AIM-9L Sidewinder air-to-air missile it will enable its fighters to perform all-aspect intercepts, they add. With their present heat-seeking Sidewinders, they are forced to maneuver behind enemy aircraft to attack them. The external fuel tanks and KC-707 aerial tankers included in the arms package approved Oct. 28 will permit Saudi F-15s to be based in portions of Saudi Arabia out of range of attack from across the Persian Gulf.
US-made AWACS and aerial tankers in Saudi Arabia also increases the effectiveness of US forces deployed to the region in an emergency by providing a logistics base and support infrastructure they could use, analysts say.
A Senate Foreign Relations Committee report recently noted that although Saudi Arabia is not inclined to provide the US with bases, ''many in the Defense Department are convinced that continued military cooperation will afford the United States the possibility of base use, or at least (with the opportunity) to share facilities in a crisis.''
Although the Pentagon refrains from discussing the use of Saudi bases for fear of offending Riyadh, it clearly expects to use them should the US become involved in a regional conflict. From the desert kingdom US aircraft could launch sorties deep into Iranian, Afghan, and Soviet territory.
From a foreign policy perspective, analysts contend a defeat would have sapped his efforts to forge a strategic bulwark in the region against any ambitions the Soviet Union might harbor for the area. They also claim that it would have displayed irresolution to the world that could only dismay allies and encourage foes.
US Defense Secretary Caspar W. Weinberger long has claimed that approval of the arms package to Saudi Arabia will go a long way toward convincing other Mideast nations that the US is a reliable partner, thus enabling those countries to take the ''political risks'' necessary to achieve a durable peace in the Middle East.