U.N. officials are hoping that the American hostages in Tehran will be moved within a few days from the occupied U.S. Embassy to meet with the international commisssion investigating Iranian grievances, diplomatic sources said yesterday.

Such a meeting with the commission appointed by the United Nations could serve as a pretext for transferring the hostages from the hands of their mililtant captors to the custody of Iranian authorities, the sources said.

The commission's mandate, carefully constructed by U.N. Secretary General Kurt Waldeheim, calls for interviews with each of the estimated 50 Americans who have been held in the embassy since it was seized by the militants 16 weeks ago.

Although the panel reportedly has desscussed the hostage interviews with Iranian authorities since arriving in Tehran on Saturday, its plans to meet the Americans have been clouded by persistent opposition of the embassy occupiers.

A spokesman for the militants repeated that opposition last night, saying in an interview with Reuter, "This commission has come to investigate the crimes of the shah and the United States . . . they have not come here to visit the hostages."

Despite this adamant opposition by the millitants, U.N. officials are hoping that Iranian President Abol Hassan Bani-Sadr can break the resistance and make good on his private assurances to Waldheim that the hostages would be released soon.

But diplomatic observers doubt whether Bani-Sadr can influence the militants without support from Ayatollah Ruhollah Khomeini, Iran's revolutionary leader who controls the militants and has lavishly praised them in recent statements.

Sources cautioned, however, that U.N. authorities may be engaging in wishful thinking to offset a series of recent setbacks, highlighted Saturday when Khomeini said the terms for release would be decided by Iran's new parliament, which is not expected to meet until April.

Further dampening hopes Tuesday, Ayotollah Mohammed Beheshti, secretary of the governing Revolutionary Council, said the parliament probably would not begin its debate on the hostages until May because of likely organizational problems.

Secretary of State Cyrus Vance declined to predict yesterday when the hostage would be freed.

"I cannot tell you when that is going to be," Vance said at a news conference held primarily to report on his meetings with the foreign ministers of Australia and New Zealand.

Amid these dark diplomatic signs, U.N. and U.S. officials are pinning their hopes on a possible commission meeting with the hostages as a pretext for removing the Americans from the embassy complex in central Tehran.

At the United Nations yesterday, U.N. spokesman Rudolf Stajduhar said the the panel of five lawyers hopes to meet the hostages "very soon." Another official said a meeting could come as soon as "a few days, maybe a week."

A U.S. official deeply involved in the negotiations said the commission's meeting with the hostages is "a key element" in testing Bani-Sadr's ability to follow through on his general assurances that the hostages would be freed.

"It's one of those hallmarks on a foggy road to see if you're on that foggy road," he said. "If the Iranians forbid the commission to see the hostages, that would be an important defiation from the Waldheim understanding."

When he publicly unveiled the inquiry commission last week, Waldheim announced that the panel would speak to each of the hostages. In his prepared remarks, he said the interviews would be conducted "at the request of the Iranians."

American officials also have long been eager for international observers to take an inventory of the captives and report back on their health and living conditions. Unitl now, the Iranians have limited visits to persons acceptable to the militants.

Proposals to transfer the hostages to the custody of a third party, such as the International Red Cross, have been made since Waldheim began trying to convince Washington and Tehran to accept his plan for ending the crisis.

But informed sources all but rule out a role for the Red Cross, saying that the militants would give up their captives only to Iranian armed forces or the Revolutionary Guards organized by Khomeini after last February's revolution.

In past interviews, Bani-Sadr said he might have "Iranian authorities" take control of the embassy from the militants. Although he says he would avoid a forceful clash with the militants, he has the power to call in the armed forces.