The head of the Iranian National Oil Co. told a nationwide radio audience there last week that Iran may now be able to sell, at a profit, some of the heating oil ordered sold to that country by President Carter for humanitarian reasons.

The Carter administration is seeking clarification of the statements in the Tehran radio broadcast, a spokesman said.

"We expect a denial based on the facts," he said, adding that the United States had been assured that the fuel would be used by Iran for "internal purposes only."

In the broadcast, Hassan Nazih said that if construction of a major Iranian refinery at Isfahan is completed soon enough the emergency shipment of 2 million barrels of kerosene and No. 2 heating oil from the United States will not be needed.

Nazih told his audience that two months ago the Iranian government thought it might need the fuel because it was unsure of the completion date for the refinery.

"But since the Isfahan refinery will start operation within the next two or three months, we will not need the oil we have bought, and there is a possibility that we will be able to sell it at a higher price once the Isfahan refinery starts operation. I think we will be able to export some of the oil products."

White House and State Department officials yesterday sought to downplay the importance of the speech.

"It was made for internal consumption in Iran," one official said. "They are trying desperately to protect themselves from charges of mismanagement."

At the time the controversial $47 million sale was announced, Carter strove to dampen criticism by claiming that the fuels were needed for heating and cooking, and that the sale -- at a time when many New Englanders are concerned about possible shortages of the same fuel this winter -- was made for humanitarian reasons.

And in a just declassified letter from then-energy secretary James R. Schlesinger Jr. to Commerce Secretary Juanita M. Kreps describing the proposed sale, Schlesinger said, "I am informed that the Iranians have indicated to Hess [Amerada Hess, the refiner shipping the product to Iran] that these products are needed for heating and cooking purposes.

"Hess is anxious to honor the Iranian request as a means of assuring a continuing supply of Iranian crude to its Virgin Islands refinery."

Energy Department sources say Hess had been assured not only that the fuel would be used domestically in Iran, but that Hess would be allowed to fill its delivery ships with Iranian crude oil for the voyage back to the refinery.

The State Department indicated yesterday that construction of the Isfahan refinery probably will not be completed in time to supply heating and cooking products for this winter.

Thus, it said, the sale to Iran "was a sensible precaution as indicated by Mr. Nizah. The sale was also sensible from our standpoint. Two million barrels is a small fraction of U.S. refinery output, and the shipment to Iran will not reduce U.S. supplies. In fact, helping Iran meet its needs helps to assure the availability of crude oil for this country. We purchase about 750,000 barrels of crude oil a day from Iran."

At a town meeting in Tampa yesterday, Carter was asked about the Iranian broadcast.

"I don't know whether Iran needs that oil or not," he responded. " . . . The oil was sold to Iran, I understand, at the market price, and if Iran should not need it, then it probably will be sold right at the market price."

Carter said that "I'll be sure that Americans don't come up short on kerosene or home heating oil," and added that Hess "plans to help me with that."

Carter said the oil was sold to Iran "because they said they had a hardship case, and I think it was a good investment, because if we had not cooperated with them I can't claim that Iran would have cut off all oil sales to us, but they sell us a lot of oil every day. This is a one-shot proposition."

Meanwhile, Rep. Benjamin S. Rosenthal (D-N.Y.), chairman of a Government Operations subcommittee, said he plans to investigate the sale to Iran.