Iranian opposition leaders fear that U.S. policy is swinging away from seeking a negotiated political solution to the Iranian crisis and toward supporting strong military measures to restore a clearly pro-American government, an American professor in close contact with Iran's opposition said yesterday.

The professor, Richard Falk of Princeton University, returned last week from a wide-ranging interview trip that he, former U.S. attorney General Ramsey Clark and journalist Don Luce made to Iran and France at the suggestion of Iranian opposition figures, who helped finance the trip.

Describing a series of a sharply etched impressions formed during lengthy talks with the exiled Moslem leader Ayatollah Ruhollah Khomeini in Paris on Monday and with Prime Minister Shahpour Bakhtiar, U.S. Ambassador to Iran William H. Sullivan and other key figures in Tehran a few days before, Falk asserted:

A serious split continues within the Carter administration on Iran policy, and public and private statements by administration officials approving the Iranian army's harsh crackdown on demonstrations supporting Khomeini's return to Iran are stirring fresh concern that "the U.S. is backing the militarization of the conflict now."

Sullivan reportedly described the Iranian military to the three visitors as "a wounded animal, nervous, unpredictable" and probably unable now to take control of the "genuine national revolution that has driven Shah Mohammad Reza Pahlavi from the country, forever in Sullivan's view.

Bekhtiar sees Khomeini as being surrounded by covert Communist aides who would turn the country over to Soviet domination if they came to power. Bakhtiar seems to have to refer even minor decisions to some other power, probably the army. The prime minister is "intelligetn, isolated and totally dependent on the U.S."

Khomeini is eager to see "sympathetic Americans" and to tell them that despite his suspicions of the U.S. military and espionage presence in Iran, "it is not too late to develop a friendly relationship." Khomeini cannot appear to compromise in any way with Bakhtiar, but he is ready to discuss an orderly transfer of power to a post-shah government.

The most important economic planners allied with Khomeini would cut Iranian crude oil production roughly in half, to about 3 million barrels a day, if they were to come to power, to conserve future revenue. Such a step would create sharp new pressure on world oil prices.

State Department officials have emphasized that Clark, who was attorney general in the Johnson administration and an unsuccessful candidate for the U.S. Senate from New York in 1974 and 1976, and his two companions were traveling abroad as private citizens without any blessing from the administration.

Clark talked to Iranian experts at the State Department before the trip, a State Department official said. Clark, who practices law in New York and who has become associated with a number of radical political causes, could not be reached for comment on the trip.

Falk, who formed a small group known as the U.S. People's Committee on Iran about 18 months ago, will brief some U.S. officials in Washington this week.

In two lengthy telephone conversations from Princeton, where he teaches international affairs, Falk described his involvement in the Iranian crisis as an outgrowth of his work in the antiwar movement of the 1960s. Falk said his group helped bring together not only Americans interested in Iran but also Iranian dissidents living in the United States.

Even before their counterparts emerged in Iran as the forces that would join in the protests that drove the shah from the country, activist students and religious groups like the Young Moslems were talking together through Falk's committee in the United States, he said. This gave him a broad range of contacts in the Iranian opposition, and he proposed the trip to Clark and Luce.

In Iran, they worked primarily through two small nonreligious opposition parties, the Radical Movement and the Liberal Movement, which are allied with Khomeini. An Iranian businessman, Mohammed Farid, who is close to these two groups, paid their air fare, Falk said.

Falk said he was surprised that Ambassador Sullivan spoke with apparent candor about his repeated differences with Washington during an "on the record" session with the three visitors, which Falk recounted in persuasive detail.

Sullivan reportedly said he decided as early as last September that the shah should leave the country to make way for a successor government, at a time when the White House continued to see no alternative but total support for the shah. Now, Sullivan reportedly sees Bakhtiar as failing to be the final victor in the power struggle that centers on the military and Khomeini's religious forces.

Sullivan thinks that a move by the military to take control would be ill-advised now, and ecommends that the Carter administration take a low profile now, said Falk, who testified against Sullivan's nomination to the Iran post in 1977

Falk said that Iranian opposition figures he is in touch with are concerned about the "substance and symbolism" of a decision by the administration last week to pay for an emergency shipment of 150,000 barrels of diesel fuel to keep Iranian military vehicles moving during the period of confrontation over Khomeini's travel plans.

"That is being seen as intervention," Falk said. "Khomeini is extremely sensitive to the appearance of American involvement in what the army is doing to his followers."

President Carter was asked at a news conference Friday if the diesel shipment to the military constituted interference in Iran. He denied this, saying that "shipments of energy supplies, and I'm sure food and other goods, to let the people of Iran have a better life are very good and constructive and proper."

Also on Friday, State Department spokesman Tom Reston responded to questions about the Iranian army's shooting and killing demonstrators by stating regrets about the loss of life but adding: "We do not believe the political future of Iran should be determined in the streets." He stressed that "peaceful conditions should be established."

Published reports of senior but anonymous U.S. officials telling reporters that the administration had been "encouraged" by the army's actions also stirred concern about U.S. policy among the Iranian opposition, Falk said.