Iran expects conciliatory gestures from the United States when American hostages are transferred from the hands of the militants occupying the U.S. Embassy in Tehran, U.N. officials said today.

The gesture could include some public expression of regret for the Iranian grievances outlined in recent days to the special U.N. commission investigating the government of the deposed shah, Mohammad Reza Pahlavi, officials said.

Iran also expects a private message from U.S. officials signaling their readiness to normalize relations with Tehran, including resumption of shipments of spare parts and the return of Iranian assets now frozen in American banks, after the hostages return home, according to these officials.

The officials said such gestures are not part of the so-called "package deal" devised by U.N. mediators before the commission left for Tehran, but they could expedite the final release of the Americans held in Tehran since Nov. 4.

They could be pictured in Tehran as significant American concessions and make it easier for Iranian authorities to return the hostages.

[In Washington, there was extreme caution among U.S. officials assessing the latest development in Tehran. While expressing a surface note of optimism, officials noted that previous hopes that the long-running crisis was nearing resolution had been dashed. Details on Page A25.]

Officials were vague about the timing of a release. One source noted that Iranian authorities said the hostage transfer from the militants could take three days. He said the inquiry panel could take another 10 days to compile its report. No significant negotiations on the next step for the hostages -- their eventual release -- is expected until the commission's work is completed. t

Officials were publicly guarded in response to the militants' statement that they would turn over the hostages to the Revolutionary Council after their 124-day vigil.

Privately, however, officials expressed great relief at the first decisive development in the hostage crisis since U.N. Secretary General Kurt Waldheim began his mediation efforts several weeks ago.

A diplomat who visited Waldheim today described him as a "a little discouraged." The commission was "progressing very, very slowly and there was some distance between [Iranian] promises and actions," recalled the diplomat.

The U.N. chief spent all day yesterday and a good part of the early hours of today advising the commission in international telephone calls and maintaining contacts with Iranian officials. News of the dramatic turnabout came early this morning, several hours after the panel of five lawyers "had packed their bags" and prepared to leave Tehran after twelve days of hearings and collection of documents, sources said.

In the last of nine meetings they had with Iranian Foreign Minister Sadegh Ghotbzadeh, the commissioners reportedly said they had run out of patience because of persistent delays in their planned meeting with the American hostages.

Even though the visit was part of the commission's mandate reportedly agreed to in writing by Iranian officials, the militants had blocked access to the embassy for several days. Ghotbzadeh persuaded them to remain in Tehran, emphasizing the commitment of government officials to comply with the agreement carefully worked out by Waldheim, two weeks ago in talks with U.S. and Iranian officials, sources said.

While the commissioners waited with their bags packed, according to sources here, government officials pressed their argument that the nation's prestige and honor was at stake in the agreement to allow the panel to visit the hostages as part of their investigation.

It was their ability to make that point with revolutionary leader Ayatollah Ruhollah Khomeini that led to the development, according to sources.

Khomeini, the ailing national leader, is the only Iranian with control over the militants. Once he decided to back the government, Khomeini sent his son, Ahmed, to tell the militants to give up their embassy occupation, sources said. Ahmed Khomeini has served as a liaison between the captors and his father since the crisis began.

The militants, who said they would resist a visit by the commission unless ordered by Khomeini, finally decided to give up their stand after long debating sessions and pleadings by the religious leader's son, sources said.