Secretary of State Alexander M. Haig Jr. is putting out the word that mistakes by the Pentagon are responsible for some of the growing difficulties of the proposed sale of sophisticated military aircraft to Saudi Arabia.

Haig's version of the tangled Saudi aircraft deal was made known as the Reagan administration approached a decision to postpone all or part of the controversial deal in order to avert rejection of the plan on Capitol Hill. In an interview yesterday with ABC television, Haig said congressional disapproval of the aircraft sales "would represent a grievous setback in American relationships with Saudi Arabia."

As the political difficulties have mounted, various individuals and departments within the administration have begun to distance themselves from responsibility for decisions to press ahead with the aircraft deal, especially the sale of five highly sophisticated AWACS reconnaissance airplanes.

Haig's contribution came at a breakfast meeting yesterday with several diplomatic reporters. Some of his comments originally were "on the record," but later the State Department insisted that none of the secretary's remarks be attributed to him directly.

James McCartney, of Knight-Ridder Newspapers, one of the reporters who attended the breakfast, wrote that "Haig is known to believe that the Israelis have a legitimate complaint about (the) controversial new aircraft sales package for Saudi Arabia because the United States did not tell them about it in advance."

"Haig believes that a mistake was made and that the Pentagon is responsible," McCartney reported.

McCartney's account went on to report that the Israelis initially had been told the administration was considering selling the Saudis smaller and less sophisticated reconnaissance aircraft, "but they learned two weeks ago that the actual plan, put together in the Pentagon, called for the sale of five highly sophisticated airborne warning and control planes, known as AWACS."

"Pentagon officials, Haig believes, went ahead on their own to sew up the Saudi arms deal without consulting top civilian officials in the administration," according to McCartney.

The conflict within the administration about how and when to proceed is reported by various sources to have come to a head in a National Security Council meeting at the White House April 1, two days before Haig's departure on a whirlwind trip to Israel, Saudi Arabia and other Middle East and European nations.

In most of these accounts, Haig is depicted as having been more cautious about quick decisions on the Saudi sales than was Secretary of Defense Caspar W. Weinberger or military officials. Haig reportedly was concerned about the Israeli reaction and the political problems of the aircraft sales package on Capitol Hill.

The Pentagon, on the other hand, is reported to have already worked out the AWACS sale on a tentative basis in Washington discussions with a high-ranking Saudi Air Force official, Col. Fahd Abdallah. The Air Force is reported to have been particularly anxious to sell AWACS to the Saudis to help defray the high cost and increase the production run of the sophisticated plane.

Israeli officials had indicated that they might not make a serious fight against other elements of the proposed Saudi sales package, such as range-extending fuel tanks and air-to-air missiles for the F15 warplanes provided by the U.S. But the AWACS, with advanced radars capable of monitoring Israeli military air traffic, presented a greater military concern to the Jewish state and a more powerful political issue.

Former Israeli Foreign Minister Abba Eban, making this point to reporters who accompanied Haig to Israel two weeks ago, said "the idea of Arab eyes scrutinizing us is scary."

Officials on all sides of the policy debate have conceded there was little attempt before the April 1 decision to explore the congressional reaction. Had this been done, it seems clear, the Reagan administration would have been much more cautious.

In his ABC Television interview, Haig told correspondent Barrie Dunsmore that no decision has been made about when to submit the Saudi sales to Congress, and he seemed to hint that the administration would not go ahead until it was confident of support. "I don't think we will proceed on the assumption that we're going to lose," he said.

Asked about his relationship with senior White House advisers, Haig said they are "very, very good at the moment."