The Reagan administration, in the face of strong policial opposition, may now postpone sending Congress its controversial package of new military aircraft sales to Saudi Arabia, informed sources said yesterday.

A final decision on the issue, which has large-scale diplomatic as well as political repercussions for the administration, is not likely to be made before Senate Republican Leader Howard H. Baker Jr. (Tenn.) and a delegation of eight other senators return this weekend from visits to Saudi Arabia, Israel and other Middle East states, the sources said.

Nevertheless, it is clear that White House officials as well as some of the State and Defense departments have become alarmed at the darkening legislative prospect of the planned arms package, which includes range-extending fuel tanks for U.S.-supplied F15 warplanes, air-to-air missles, airborne tankers and five highly sophisticated airborne warning and control system reconnaissance aircraft.

The last element in the package, the sophisticated AWACS radar planes, is the one that has raised the strongest opposition of the Israeli government and of a number of American lawmakers. Secretary of State Alexander M. Haig Jr. was informed by Israeli leaders during his visit to Jerusalem early last week of their intention to make an all-out fight against the AWACS sale.

Later on the same trip, Haig reiterated to Saudi leaders the administration decision to ask Congress for approval of the four-part military aircraft package, including the sale of the AWACS. The Saudis already had been informed officially of the decision, approved at a National Security Council meeting on the eve of Haig's departure for the Middle East, by a message from Defense Secretary Caspar W. Weinberger to Prince Sultan, the Saudi defense minister.

The administration is reported to have tentatively decided at the April 1 NSC meeting to submit the Saudi arms sales package to Congress shortly after its return from its current Easter recess April 27. However, no date was offiically given to the Saudis, sources said, and thus a deferral of all or part of the arms package would not be a demonstration of bad faith on the part of the administration.

A senior official emphasized that there is no inclination within the high reaches of the administration to reverse the decision to make the sales, but neither did the minimize the political difficulties that have arisen. It would be a catastrophe, the official said, if the Saudi package were sent to Congress and rejected, as the lawmakers have a right to do by majority vote in both houses.

The catastrophic consequences were not spelled out, but these would certainly include a loss of credibility with the important oil kingdom and other Arab nations and, at home, the repudiation of one of the administration's earliest foreign policy decisions.

Another top-level meeting of administration officials were reportedly convened late yesterday to consider the Saudi sales program, but there was no word of a definitive conclusion.

One option reported to be under discussion within the administration is deferral of the entire Saudi aircraft package until midsummer, following the June 30 national election in Israel. The proposed U.S. sales and the political maneuvering around them in Washington could affect Prime Minister Menachem Begin's struggle to remain in office. Administration sources also noted that nearly all Israeli factions will be compelled to take a strong stand against the Saudi sales while the competition for votes continues.

A midsummer submission to Congress, however, could add another burden to the adminstration's top-priority effort to obtain passage of its budget and tax proposals, which are expected to face their legislative showdown in late July or early August.

Another option said to be under consideration is deferring the proposed sale of AWACS while sending to Congress most of the rest of the Saudi aircraft package.

Under current proposals, the Saudis would not receive the first of their sophisticated reconnaissance planes until late 1985, and so a delay of a few months would have little practical importance. However, to split off the AWACS for later consideration would be a signal of politcal weakness, and the administration under this plan would have to fight two legislative battles over the Saudi aircraft sales instead of one.

Military aircraft are the most sophisticated and highly visible items of American material supplied to the Saudis but they are far from the only ones. The administration was reported by the Association Press to have decided to sell 12 ground radar stations and 10,000 antitank missles to the Saudis. Administration officials, while not denying that such sales have been under discussion, said no final decisions have been made.