A United Nations panel going to Tehran this weekend to investigate the alleged crimes of the deposed shah will interview each of the Americans being held hostage, U.N. Secretary General Kurt Waldheim said today.

The last-minute change in the five-man panel's plans reportedly was demanded by Iranian authorities to appease the militant captors, who have claimed that many of the Americans they are holding at the U.S. Embassy in Tehran are spies.

[Iranian revolutionary leader Ayatollah Ruhollah Khomeini in a message broadcast by Tehran radio early Thursday, appealed to Iranians to continue to demand the extradition of the deposed shah and attacked the United States for its "criminal interference" in Iranian affairs. The broadcast did not mention the hostages.]

Until midday, the five-man investigating panel, which had already gathered in Geneva, had been expected to fly to Tehran today. For what Iranian officials described as "technical reasons," however, the panel's departure was put off until the weekend.

In a short press briefling, Waldheim insisted that "no deadline" has been set for release of the estimated 50 Americans. He decided to say whether he has received informal assurances from the Iranians that the hostages would be freed at some stage in the inquiry process.

"Evidently, the whole purpose of this effort is to find a solution to both grievnaces," the U.N. chief said, referring both to U.S. demands for the release of hostages and Iran's insistence on a public airing of its complaints against the deposed shah, Mohammad Reza Pahlavi.

In a brief written statement, Waldheim gave a vague description of the commission's mandate, saying it would "undertake a fact-finding mission . . . to hear Iran's grievances and to allow an early solution to the crisis" that has lasted 15 weeks.

U.S. officials sought to narrow the commission's scope to investigating alleged crimes of the deposed shah, but the panel's cochairmen reportedly insisted on a more open-ended mandate to give the group enough latitude to conduct a fiar and complete inquiry.

In Tehran, Iranian President Abol Hassan Bani-Sadr released a copy of his long-awaited message to Waldheim in which he said that a "court of inquiry" would investigate "past American intervention into Iran's internal affairs" during the former shah's rule.

Bani-Sadr's references to a past American policy and another statement that the inquiry would cover what he termed the "treacheries, crimes and corruptions" of the shah and the United States caught Waldheim by surprise and forced him to seek last-minute clarifications, sources said.

While the U.N. chief was clarifying Bani-Sadr's language, the five commission members who had assembled at the airport in Geneva for a flight to Tehran turned back as it became clear that Waldheim had to delay his announcement of their mission.

Names of the commission members have been known since Sunday, but Waldheim has been unwilling to officially announce them and launch the mission until receiving written approval from Bani-Sadr. The panel consists of Mohammed Bedjaoui of Algeria, Andres Aguilar of Venequela, Louis-Edmund Pettiti of France, Adib Daoudi of Syria and Hector Jayewardene of Sri Lanka.

Bani-Sadr's final communique was unavailable, and Waldheim pointed to the Iranian president's vague statement on the panel's mandate when asked if it would investigate past U.S. behavior in supporting the deposed shah.

At his briefing, Waldheim said Bani-Sadr appealed for a postponement until this weekend of the commission's arival to give Iranian authorities more time to "make sure the commission is well received and doesn't run into complications." Sources said Bani-Sadr may have asked for the delay to shore up his position at home and solidify his support from Khomeini, who controls the militants occupying the embassy.

The Iranian ambassador to the United Nations, Mansour Farhan, who is in Geneva, told special correspondent Anne Crosman that Iran is eager and willing to receive the commission. But he said the delay was needed to give Iran time to prepare accomodations for the commission and to gather evidence and documents to present to it.

Bani-Sadr has given Waldheim general assurances that the ailing religious leader would publicly endorse the commission and call for a hostage release at some stage of the inquiry, thus signaling the militants to end their long vigil.

Before leaving New york this week, the commission's cochairmen, Bedjaoui and Aguilar, told associates they expected to receive a firm commitment for a release of the Americans within a week after they began their investigation in Tehran.

But Bani-Sadr and Iranian Foreign Minister Sadegh Ghotbzadeh have said that the hostages world remain in Tehran until the commission completed its work -- a period expected to last two weeks, according to remarks made by Waldheim in an Austrian newspaper Tuesday.

In consultations with members of the U.N. Security Council yesterday Waldheim indicated that the timing of a release has yet to be set, according to sources.

"Everybody's holding their breath,' one U.N. official said. "Nobody is absolutely certain that Bani-Sadr can pull this off. But they've got to try. It's the only game in town."

Once the commitment for a hostage release is made, sources said, Iranian armed forces would take control of the 24-acre embassy under the supervision of a third party, such as the International Red Cross. Bani-Sadr was appointed commander of the armed forces yesterday, giving him the power to order such a transfer.

When Walhdeim was asked if the commission's interviews with the hostages would be extensive, he said the decision would be left to the commission.

Waldheim refused to say whether the commission's work was linked to the timing of the hostage release, responding that "both aspects of the problem have been taken into account."