The Reagan administration yesterday abruptly postponed until today the scheduled formal submission to Congress of its proposed $8.5 billion sale to Saudi Arabia of sophisticated radar planes and other aircraft equipment.

The postponement touched off intense speculation about whether the administration is planning a last-minute maneuver, possibly involving a revision of the sales package, aimed at preventing what appears to be a near-certain congressional veto of the deal.

However, congressional sources said that, as of last night, even the Republican leadership, which met with President Reagan yesterday morning, did not know what had caused the delay.

Late last night, Sen. Charles H. Percy (R-Ill.), chairman of the Senate Foreign Relations Committee, said notification of the sale would be submitted formally to his committee at 8:45 this morning.

The sources said the first indication of administration intentions is likely to come shortly thereafter, when Secretary of State Alexander M. Haig Jr. testifies before the committee about the proposed sale of Airborne Warning and Control System (AWACS) planes.

In the meantime, administration officials refused to give any explanation for the confusing series of events revolving around the White House yesterday.

First, Haig canceled meetings at the United Nations with six foreign ministers, and hurried back to Washington for consultations with senior White House officials. Then the administration announced that the notification to Congress was being delayed.

Once notification is made, the sale can be blocked if both houses of Congress vote against it within 30 days.

The administration privately has conceded defeat in the Democratic-controlled House, and a majority of senators appears inclined to oppose the sale because of concern that present arrangements do not give the United States sufficient control over the AWACS planes to prevent their use against Israel or possible capture by U.S. foes.

That was conceded by Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) after the leadership meeting with Reagan yesterday. He told reporters, "We don't have the votes." He added, though, that "it's not beyond salvaging," and said that, eventually, "I think Ronald Reagan's going to get the AWACS through."

Any hope of rescuing the deal rests on whether the administration can overcome Senate concerns about the control question by winning Saudi approval for a compromise formula that would include the presence of U.S. military personnel on all AWACS flights. Until now, the Saudis have rejected joint-crew proposals as an infringement of their sovereignty.

However, active negotiations about a compromise are being conducted in Saudi Arabia by the new U.S. ambassador, Richard W. Murphy, who traveled to the Persian Gulf kingdom Monday.

As a result, most speculation about the notification delay centered on whether it was connected to Murphy's continuing talks, and the possibility that he might be making some headway toward a revised sales agreement.

White House deputy press secretary Larry Speakes, who announced at midday that the notification would be delayed for as long as 36 hours, said Haig had returned early primarily to prepare for his Senate testimony and to brief Reagan on foreign policy issues for today's presidential news conference.

But Speakes also said Haig was participating in discussions on the AWACS controversy, and other sources said they believed he had been in contact with Murphy.

Congressional sources said the only thing of which they were certain was that something happened during the day to cause the administration to back off from its stated intention to make the notification yesterday.

They said Baker's office was told by the White House around noon yesterday that the notification would arrive later in the day, and learned shortly afterward about Speakes' announcement of a delay.

Amid all of the confusion, the president ran into some static from an unexpected source: his elder daughter, Maureen, announced in San Francisco that she opposes the AWACS sale in its present form because it does not provide for adequate U.S. control. She is an unannounced candidate for the Senate from California.