Libyan leader Muammar Qaddafi said today that he would ease his anti-American stance this year because of "promises" from President Carter to "radically change American policy in the Middle East" if he is reelected to a second term.

The friendlier Libyan mood toward the United States during this election year, Qaddafi indicated, constituted Washington's "last change" to avoid a serious oil sales embargo. Libya provides an important portion of U.S. oil imports.

Qaddafi, in an interview with journalists here, pointed out that Libya recently broke off economic relations with China in retaliation for Chinese shipments of arms to Egypt.

While the United States is also supplying Egypt with weapons, Qaddafi said, he has not ordered a similar retaliation against Washington because of his desire to give Carter a "last chance."

[A high White House official said President Carter had made "no commitments direct or implied about a radical change in American policy" in the Middle East. Carter, in recent messages to Qaddafi, has simply expressed "an interest in improved relationships," a White House source said.]

Libya, one of the foremost radical Arab states, is a leading supporter of the Palestinian movement and a chief opponent of the Camp David peace accords and the Egyptian-Israeli treaty that followed.

Qaddafi has opposed U.S. efforts to bring about peace between Egypt and Israel and any negotiated settlement in the Middle East, calling instead for immediate return of the occupied territories to full Palestinian control.

The Libyan ruler said he preferred Carter over Sen. Edward M. Kennedy D-Mass.) or any other candidate in the U.S. presidential race.

"Whatever happens, any American president will be under Zionist influence," he said, but "because President Carter has promised to make changes in American policy, we prefer Carter be given a chance to see if he keeps his promises."

Asked who had made the promises and what form they had taken, Qaddafi replied that "almost precise promises" were involved.

"As I understood," he said, "I believe President Carter promised to radically change American policy in the Middle East." Qaddafi insisted he was speaking on the basis of "not just general statements," but he refused to explain his remarks further.

Libya sells about 40 percent of its daily oil production of 2 million barrels to the United States. This amounts to about 10 percent of U.S. imports but the Libyan crude is a high quality, low sulfur petroleum especially suited to use as gasoline.

Although much of the interview dealt with U.S.-Libyan relations, Qaddafi showed little of the rancor or anti-American vehemence with which he has often spoken of the United States in the past.

"Because it is an election year," he said, "it is better to cool it."

Despite Libya's frequent threats to embargo oil sales to the United States and the burning of the American Embassy in Tripoli last month. Qaddafi said that the responsibility for improved relations "rests with the United States."

"They do us injustice, they put us on the black list," he said, in apparent reference of U.S. Congressional pressures against delivering American-made military transports and Boeing 747 jumbo jets to Libya.

"The Libyan peoples have done nothing up to now against the United States," he said. "If they miss this chance and do not change policy, this is the last chance."

Although he seemed confident and forthright in discussing the United States, the 38-year-old military strongman showed clear uneasiness when questioned about the invasion of Afghanistan, a fellow Moslem country, by the Soviet Union, which enjoys enormous official influence here.

Outwardly subdued, the often flamboyant Qaddafi said, "I do not have enough information" about the Afghan situation.

When pressed by reporters, he laughed nervously and said, "We have talked enough about this subject."

On other matters, Qaddafi:

Refused to endorse suggestions from the recently concluded General Peoples Congress, the highest instance of his experiment in direct democracy, that Libya cut back its oil production by 36 percent.

Insisted that "nothing negative happened" that would explain the nearly two-month delay in exchanging charges d'affaires with Iran. Part of that agreement called for joint investigation into the disappearance of Imam Moussa Sadr, the leader of a Moslem sect in Lebanon. Libya has insisted Sadr left here for Italy after a summer 1978 visit, but a Moroccan newspaper charged he was executed near Tripoli after Libyan officials misinterpreted orders.

"The situation in Iran is not yet stable," Qaddafi said. "Responsibility in Iran is not well defined."

Indirectly denied suggestions that Libya was trying to arrange a negotiated settlement in the war over the Western Sahara pitting Morocco against the Polisario guerrillas-backed by Algeria and Libya. "How does the war end," Qaddafi asked, "if the king (Hassan) of Morocco insists on oppressing the Sahrawis" as the people of Western Sahara are called, "and integrating this part" of the former Spanish territory "by force" into his kingdom. "This is a revolutionary explosion, not a matter of negotiations."