U.N. officials expressed cautious optimism yesterday that an Iranian announcement late Saturday night accepting an international inquiry into the affairs of the deposed shah represents a key step in resolving the U.S. hostage crisis, now in its 92nd day.

The announcement by the Revolutionary Council in Tehran, followed by statements by an Iranian Foreign Ministry spokesman yesterday, left U.N. and U.S. officials with the clear impression that there has been some movement on the part of the Iranians.

Just what that movement means was less certain, however.

"We've seen the stories but we don't know the meaning of it," said one U.S. official. "Some points are consistent with the secretary general's proposal about the commission but others are not. . . ."

U.N. Secretary General Kurt Waldheim has proposed the establishment of an international commission of inquiry that would probe the affairs of the shah but linked its start to the turning over of the hostages to a third party, such as the International Red Cross.

A spokesman for Iran's Revolutionary Council announced late Saturday night that the council had accepted the idea of an international commission.

Yesterday, Foreign Ministry spokesman Nassirosadat Salami said that Iran's revolutionary leader Ayatollah Ruhollah Khomeini also had agreed to the idea and added that the commission members would be accepted by Waldheim and would include Iranian and foreign representatives, according to an Associated Press report.

It is believed to be the first time the top Iranian leaders have publicly endorsed the idea of a commission, although Waldheim said he had been given such assurances during his visit to Tehran in early January.

Salami did not say when the commission would come to Tehran nor when hearings might begin.

U.N. officials said in New York that the Iranian decision to make an announcement on the commission is a "positive" sign, and they characterized the claim that Khomeini has endorsed it as even more important.

A State Department spokeswoman in Washington was more reserved, saying only that the department's Iran working group had seen the reports but "there is nothing we have to offer as to whether this brings us any closer to a solution to the hostage situation."

Waldheim met with Iranian Ambassador Mansour Farhang Saturday night and also with U.S. Ambassador to the United Nations Donald McHenry, although both U.N. and U.S. officials insisted that these contacts had not moved the issue beyond the generally known proposals of Waldheim's package deal. Waldheim also has been in touch with Iranians of greater authority than Farhang, although reportedly only in the "most rudimentary" type of discussion.

The militants holding the hostages said they were aware of the council's decision, according to the AP report, but a spokesman at the embassy declined immediate comment.

In a television interview yesterday on ABC's "Issues and Answers," President-elect Abol Hassan Bani-Sadr made mention of an international tribunal, but placed greater emphasis on U.S. gestures of support for the new government in Tehran and its aims.

This, along with statements by the official Pars news agency in Tehran that a "special delegation" of Americans would arrive in Tehran this week at the invitation of the militants, added to the general confusion about just what is happening in Tehran.

"The Iranians invited a slew of Americans over there next week," said an American official, "but today's report of the Foreign Ministry statement clearly points to the appointment of a commission by the secretary general, so it does not seem to refer to those Americans. What is inconsistent is that it talks of Iranians on the commission and this is the first we've heard of that."

American Indian leader John Thomas and the Rev. John Adams arrived in Tehran yesterday with mail for the hostages, according to a UPI dispatch, but it was not clear whether they are part of the "delegation" the Iranians reportedly have invited.

The latest flurry of developments comes at a delicate time politically for Iran, with Bani-Sadr scheduled to take his oath of office before Khomeini today, but with his powers still being challenged by some within the Revolutionary Council and by the militants.

U.N. officials cautioned that much of the movement back and forth on the hostage-commission issue could reflect jockeying for power among the Iranian factions.

The spokesman for the Revolutionary Council, Hessan Habibi, an unsuccessful candidate for the presidency, challenged Bani-Sadr's claims that he has the right to form a provisional government before next month's parlimentary elections.

Habibi, according to a report by Agence France-Presse from Tehran, said the council had not endorsed the step and since its power flowed from Khomeini, Bani-Sadr could not form a government.

Bani-Sadr, anxious to consolidate his power following his landslide election victory, responded in a newspaper interview yesterday that his popular mandate in the vote gives him the right to form the government.

The issue could be a crucial element in the meeting between Bani-Sadr and Khomeini today. Khomeini remains in a Tehran hospital where he is under treatment for a heart ailment and his doctors have ordered him to reduce his work load further for another two or three weeks.

The militants at the embassy, meanwhile, suddenly canceled a mass rally they had called for Monday as a means of demonstrating that they still have widespread support within Iran.

The rally apparently was canceled to prevent it from coinciding with the unofficial inaugural speech Bani-Sadr is to make at Tehran's Behesht Zahra cemetery, according to a Reuter report from Tehran. The militants said they were still calling for demonstrations of support in provincial cities, however.

The sudden about-face by the militants reflected what many in Tehran have seen as growing signs of isolation on their part.

The Manchester Guardian reported yesterday from Tehran that the militants had published an open letter to Khomeini appealing for moral support.

The letter said that in the short space of time Khomeini had been in the hospital they had come under attack from "beggars . . . who sometimes also have ambitions of leadership" and who have threatened "to smash us into pieces."

The letter included a strong reassertion of their demand that the United State should return the shah and his wealth as a precondition for obtaining the release of the hostages.

In his television interview yesterday, Bani-Sadr said he believes the militants would respond to his decisions "if there is a situation where I deem it necessary to say something to them."

His statements on the future of the shah shopped far short of the militants' outright demands for his return, however.

Speaking through a translator, Bani-Sadr said the hostages could be freed if the United States takes several steps:

Renounces "its past policy" of "intervention into the affairs of our country" and criticizes "that policy;"

"Accepts our right" to bring the "criminals" and "people who have plundered our wealth" to Iran;

And helps Iran "in practical terms" in its dealings with the shah.

Just what he meant by help in "practical" terms was unclear, although he later mentioned a legal move to obtain the wealth of the shah that is in the United States.

Bani-Sadr went on to say that the right of extradition was more important than a tribunal, a point that raises questions about his position on the international commisssion of inquiry being the key to the hostage issue.

Other observers noted that Bani-Sadr insisted only on the "right" of extradition and was more vague on the U.S. role in any proceedings against the shah.

On other issues, Bani-Sadr said:

He generally favors the return of American journalists to Iran, although he said he had noted a change in opinion in the United States since they were forced out.

He would not send Iranian troops to aid Afghan rebels but would not oppose Iranian "people" who might want to go to fight against Soviet forces in Afghanistan. CAPTION: Picture, Abol Hassan Bani-Sadr . . . seeks to consolidate power; Picture 2, Loudspeakers blared anti-American slogans, but crowds were absent from U.S. Embassy in Tehran Saturday. UPI