The administration is preparing to turn all of its big guns, including the heavy involvement of President Reagan, into the battle with Congress to win approval of a plan to sell Saudi Arabia five early-warning radar planes.

Informed sources say the president has personally told Secretary of State Alexander M. Haig Jr. that he is determined to win the fight over the airborne warning and control system (AWACS) in Congress, even though a majority of senators and representatives have signed letters or resolutions opposing the sale and the formidable Israeli lobby in Congress is working hard against the plan.

Those supporting the administration argue that if the United States cannot deliver on its pledge to the Saudis, it will be a grave setback to the U.S.'s Middle East policy, turning moderate Arab states away from the United States and opening opportunities for Soviet involvement in the region.

Opponents argue that the planes are a threat to Israel and are not needed by the Saudis.

Max L. Friedersdorf, the White House official in charge of congressional liaison, told a breakfast meeting of the U.S. Chamber of Commerce yesterday that the administration expects to informally notify Congress by letter on Aug. 24 that it intends to go ahead with the sale.

The informal notification stands for 20 days. After Congress returns Sept. 9, formal notice will be sent and Congress will have 30 more working days to try to block the deal. Both houses must disapprove of the sale to block it.