President Reagan's ambassador to Saudi Arabia, Robert G. Neumann, has been ousted at the insistence of Secretary of State Alexander M. Haig Jr. after making "indiscreet remarks" about Haig to a senator, informed sources said yesterday.

Neumann's surprise resignation after two months in office was attributed to "personal considerations" in the official announcement made yesterday afternoon by White House spokesman David Gergen. Gergen denied that policy differences within the administration were involved, and said he did not know if there had been personal differences.

Gergen also said that Neumann "was not fired; he has resigned." But others put a different construction on the departure of Neumann, who had served as an ambassador to other countries in previous administrations and was the head of the Reagan transition team at the State Department.

The problem arose, according to sources who declined to be identified, from a call by Neumann on Monday morning, July 20, to Sen. Charles H. Percy (R-Ill.), chairman of the Senate Foreign Relations Committee. Neumann, who was back from Saudi Arabia for consultations, is reported to have said that a Haig appearance on television nearly made him "throw up."

Upon learning of Neumann's comment, Haig called in the ambassador last Thursday for a tongue-lashing, but apparently gave no indication that he was seeking Neumann's resignation.

Sometime last weekend, according to the sources, Neumann was presented with the demand that he resign or be fired.

Neumann, 65, a former ambassador to Morocco and Afghanistan, was a foreign policy adviser to the Reagan presisential campaign as well as chief of the State Department transition team after November's election.

United being named to the Saudi post, one of the most important for U.S. diplomacy, he was vice chairman of Georgetown University's Center for Strategic and International Studies, from which many officials of the new administration were recruited.

The White House announced that Richard W. Murphy, a career diplomat who is ambassador to the Philippines, will replace Neumann in Saudi Arabia. The public announcement of Murphy's appointment was prepared in such haste that two posts of his previous service were misspelled, including Jidda, the diplomatic capital of Saudi Arabia, and a correction had to be issued.

Haig, questioned by reporters after a hearing of the Senate Finance Committee, said Neumann had resigned "for personal reasons," which he refused to describe. Haig denied reports that there had been a dispute about the timing of the submission to Congress of the administration's proposal to sell sophisticated airborne warning and control system (AWACS) aircraft to Saudi Arabia. Percy described his conversation last week with Neumann as unremarkable, saying that no remark about Haig laft a lasting impression.

According to one account, the ambassador's remarks concerned Haig's appearance the previous day on ABC-TV's "Issues and Answers," during which Haig declined to link recent Israeli bombing raids in Lebanon and U.S. shipments of F16 warplanes to Israel. Later the planes were impounded because of the Lebanese fighting.

Neumann, according to several sources, called for a strong U.S. reaction to the Israeli action, citing its impact in Saudi Arabia and the rest of the Arab world.

Percy said he did not recall a mention of the television program by Neumann, and denied widespread reports that he had discussed Neumann's views in a conversation with Haig.

Neumann was not available for comment yesterday. Nor were three other participants in the Percy-Neumann meeting: Graeme Bannerman of the Senate Foreign Relations Committee, Roger B. Merrick of the State Department's Saudi desk and Betsy Warren, a State Department congressional relations official.