The point man in the effort to win congressional approval for the sale to Saudi Arabia of five sophisticated radar planes known as AWACS said yesterday that the administration is "making substantial headway."

National security adviser Richard V. Allen spoke to White House reporters as the administration stepped up its lobbying effort for the sale of the airborne warning and control system planes. Allen said he believes that some congressmen's minds have been changed by hearing the administration's case.

Reluctant members of Congress are being told that a secret agreement between the United States and Saudi Arabia would prevent the Saudis from using the radar planes against Israel. They also are being told by administration representatives that there is little danger the planes will fall into hostile hands and that the sale is crucial to U.S. relations with Saudi Arabia, America's principal foreign oil supplier.

Several members of Congress said after leaving briefing sessions that they remained unconvinced, but Allen said: "Now that the administration is beginning to make its case, many of the members are hearing the arguments for the first time. We're making substantial headway."

The $8.5 billion sale, which includes air-to-air missiles, enhancements for the Saudis' F15 fighters and other equipment, will go ahead Oct. 30 unless both houses of Congress turn it down before then.

A large number of senators and congressmen went on record last spring with misgivings about the sale. Some congressional opponents of the sale have said a majority is available in both houses to block the sale, but those head counts are in dispute.

Israel strongly opposes the sale, arguing that the AWACS planes could monitor air movements inside Israel during a time of crisis. Saudi Arabia is a major bankroller of the Palestine Liberation Organization and a declared enemy of Israel.

The administration thinks it has a better chance of winning approval in the Senate than in the House.

All 22 Democratic members of the California congressional delegation announced their opposition to the sale yesterday. They released a letter from 12 F15 fighter pilots, who are stationed at Holloman Air Force Base, N.M., objecting to sale of the Sidewinder air-to-air missiles in the AWACS package.