Prime Minister Mohammed Ali Rajai of Iran said today that the United States seems ready to meet Iranian conditions for release of the American hostages, and a Moslem cleric helping formulate the conditions said the captives could be on their way home as early as Monday.

But Ayatollah Mohammed Beheshti, the influential leader of the ruling Islamic Republican Party, quickly challenged Rajai's assessment, underscoring the diffusion of authority in Tehran's revolutionary government and recalling the disappointing outcome of earlier hopeful signs from Iranian leaders.

The statements in Tehran nevertheless focused increased attention on the work of a special parliamentary commission charged with defining the final conditions under which Iran says it will release the 52 hostages, held since Nov. 4 of last year. Although Ayatollah Ruhollah Khomeini retains the final word in Iran, Rajai has declared that the commission has full power from Khomeini himself to work out the release.

Hojatoleslam Moussavi Khoini, one of seven members of the special parliamentary commisssion, made the optimistic prediction of a possible Monday release apparently on the basis of a decision setting Sunday as the date for a long-postponed debate by the Majlis, or parliament, on the fate of the hostages as determined by the commission's work.

"They could be released even the day after the conditions are announced by the Majlis," Khoini said in Tehran, according to news agency accounts. "If the Americans accept the conditions and put them into action they [the hospital] could be released as early as Monday."

But there was a public disagreement among other leading Iranian politicians whether Washington has already signaled its acceptance of the four main conditions for the prisoners' release, laid down last month by Khomeini, Iran's 80-year-old leader of the revolution against the late shah and its unquestioned spiritual and temporal leader. On Sept. 12, Khomeini announced that before the hostages could be released Washington would have to agree to return the shah's wealth, free all Iran's frozen assets, drop all legal claims against the country and promise never to interfere again in its internal affairs.

During a press conference early in the day, Rajai made his statement that he is convinced Washington is ready to meet Iran's conditions. Rajai did not specify what had convinced him. But Secretary General Kurt Waldheim of the United Nations conferred with him on the hostages last weekend in New York, the day after Waldheim was briefed on the U.S. position by Deputy Secretarys of State Warren Christopher, and there have been reports of communications between Washington and Tehran through the Swiss Embassy in Iran.

"Of course we have to explain what is meant by all the demands," Rajai said. "I was sure that they [the Americans] were ready to meet what has been brought up as the basic principles in the form of the four conditions set by the inmam [Khomeini]."

Beheshti, however, disagreed.

"The United States has not accepted the imam's conditions," he said later on. "Their statements in this regard don't show that they have accepted even those conditions that have been explained to them by the imam."

At the time Khomeini announced the conditions, much was made of the fact that he did not insist on an official U.S. apology for past involvement in Iranian affairs. That has been a condition set early on in the hostage crisis.

Rajai said later that Khomeini had simply "forgotten" to mention that previous condition. But last Saturday at the United Nations, where he went to present Iran's case against Iraq in the Persian Gulf war, Rajai said he was satisfied that the United States had already apologized, although he still expected it in writing.

Reacting to Rajai, the speaker of the Majlis, Hojatoleslam Ali Akbar Hashemi Rafsanjani, predicted today that several deputies in the 228-member Majlis will amend the commission's conditions to include the official apology. President Carter has said he will not make a formal, official apology.

Khomeini charged the Majlis with the final responsibility for resolving the hostage crisis eight months ago. But such has been its delays in taking up the issue, the internal disputes among its members about the terms to demand of the Americans and the repeated disappointments of dashed hopes for a quick resolution of the crisis, that diplomatic analysts here maintained a cautious wait-and-see attitude about next Sunday's Majlis session.

Rajai's own optimism about the upcoming debate and his expectations of Washington's ultimate acceptance of the conditions the Majlis will lay down, however, seemed to reflect the tone of Carter's recent conciliatory gestures toward Iran as well as the reported private communications through the Swiss.

Rajai seemed to be pushing for a resolution of the hostage issue as a means of breaking Iran out of its international isolation, which has complicated its diplomatic, economic and military ability to counter Iraq's invasion of its oil-rich Khuzestan Province. In fact, the Iranian prime minister declared that the hostage issue was already a dead one as far as Iran was concerned.

"The hostages are not really a problem for us," he said. "We are in the process of resolving it. The nature of the hostage-taking was important for us. We got the results long ago."

With the U.S. presidential elections only two weeks away, Carter has been willing to renew public efforts to gain the release of the hostages, originally taken prisoner by Iranian revolutionaries reacting to the late shah's entry into the United States for medical treatment.

If Iran should release the hostages, Carter said, he would unfreeze their assets of several billion dollars and drop the embargo on trade.