Hours before the arrival in Tehran today of the U.N. commission that the United States hopes will arrange rapid release of U.S. hostages, Ayatollah Ruhollah Khomeini ruled that Iran's new parliament -- which will not assemble until April -- must decide the issue.

"Since the representatives of the people will soon be meeting in the Islamic consultative assembly, any decisions on the release of the hostages and the concessions to be obtained in return for their release will be up to them," the Iranian leader said from his Tehran hospital bed, where he is recuperating from heart trouble.

Informed sources in Paris said Khomeini's new condition was not part of the still mystery-shrouded terms of reference for the fact-finding commission worked out by U.n. sEcretary General Kurt Waldheim.

Khomeini's latest pronouncement would appear to offer little encouragement for a quick resolution of the hostages' ordeal, now in its 112th day, despite hopes placed in the five-man commission that flew from Geneva earlier today after a still largely unexplained delay.

The announcement did, however, mark a fundamental change that could help resolve the crisis. Khomeini's statement that the parliament -- not the embassy militants -- will decide the hostages' fate is likely to strengthen the band of President Abol Hassan Bani-Sadr, who has sought an early release of the American diplomats and who is likely to control the new parliament.

The arrival of the panel -- lawyers from Algeria, France, Sri Lanka, Syria and Venezuela -- followed intricate negotiations among Waldheim, officials in Tehran and the Carter administration.

[Diplomatic sources at the United Nations in New York were clearly disappointed by the limits imposed by Khomeini on the hostages' release. "It was expected that shortly after the panel began that Iran would make some commitment about the hostage release," said one diplomatic source. "But this statement pushes the release too far into the future, and is not a firm commitment. The U.N. had never expected that we would have to wait for parliament to act before the release."]

On arrival in Tehran, French lawyer Louis-Edmond Pettiti told reporters that it "has not yet been decided" how long the commission would stay in Iran, according to news agency reports.

U.N. spokesman Samir Sambar said it is hoped that the commission's hearings would ease tensions between Iran and the United States.

Khomeini's statement focused at length on Iranian grievances against the deposed shah, Mohammad Reza Pahlavi, and the United States, grievances the panel is intended to probe. He urged the "dear invalids and heroes of our revolution" to attend commission meetings and make their plight known.

Iranian Foreign Ministry spokesman Nassir Salami told reporters in Tehran, however, that the panel's meetings would not be open to the public to give the panel the "privacy it needs to study the evidence and to hold proper deliberations."

Members of the panel, in addition to Pettiti, are Mohammed Bedjaoui of Algeria and Andres Aguilar of Venezuela, the cochairmen; Hector Jayewardene of Sri Lanka and Adib Daoudi of Syria.

U.S. and U.N. officials had expressed hope that the panel's work would lead to the rapid release of the hostages, but Khomeini's statement today made it clear that it could only be considered a first step.

The pro-Khomeini students at the U.S. Embassy agreed with Khomeini's statement that the fate of the hostages should be decided by the new Iranian parliament, a communique broadcast by Radio Tehran said today.

"Imam, you have given the order that the fate of the hostages should depend on the people's representatives that will meet in the parliament," the communique said.

"All our honor rests in the support that the people have always brought to us," the statement said. "We render it to the will of our good struggling people."

The first round of elections for Iran's new parliament is scheduled for March 14, with a runoff two weeks later if needed. It is not scheduled to assemble until early April.

In analyzing Khomeini's statement observers of the long-running Iranian crisis noted that for the first time Khomeini did not directly link the hostages' release to the extradition of the shah, although he reiterated Iran's persisent demand for his return.

He specifically mentioned for the first time a mechanism for the release of the estimated 50 hostages -- the new parliament. That means the Islamic militants holding the hostages at the U.S. Embassy since Nov. 4 no longer would have the final say.

The captors routinely have insisted they would obey only Khomeini and the shah's return could secure the Americans' release. Until today Khomeini had remained purposely vague about the disposition of the hostages.

However, analysts recalled that ever since the embassy was seized, hopes have been raised on the occasion of various Iranian elections.

First there were rumors the hostages would be released after the late November vote on the constitutional referendum. Similar views accompanied the Jan. 15 presidential election won handsomely by Bani-Sadr.

Khomeini softened his indirect criticism of the embassy captors by noting their prime demands -- the return of the shah and his fortune -- and said the students "had dealt a crushing body blow against the world-devouring U.S.A."

He quickly followed this, however, with his statement that it is the parliament -- not the militants -- that must decide the fate of the hostages.

Bani-Sadr has been maneuvering since his election to take hold of the strings of power in revolutionary Iran and to isolate the militants at the embassy.

In outlining his terms for resolution of the hostage issue, Bani-Sadr has not demanded the extradition of the shah to Iran, but only the recognition of Iran's "right" to extradite him and seek return of his wealth.

He also has sought a U.S. guarantee that it will not interfere in Iran's internal affairs, something President Carter did in his statement on Iran earlier this week. In addition, Bani-Sadr wants a U.S. admission and apology for previous "interference" in Iran, something U.S. officials have said they will not give.

There were no public statements by Bani-Sadr today. Khomeini, in his statement, urged Bani-Sadr and the government "to devote all their efforts and strivings" to the return of the shah and warned that "Iran is not giving up on this just demand and it will not take a single step backward."

That appeared to confirm reports that Iran still hopes to persuade Panama to extradite the shah on the basis of purely criminal charges to be presented to the Panamanian authorities within the next few days.

No extradition treaty exists between Iran and Panama. Panamanian law forbids extradition on political charges or if the accused risks the death penalty in the home country.

But informed sources stressed that the U.N.-sponsored commission and the extradition procedure in Panama were, in Iranian eyes, part of a single overall strategy.

Expressing doubts that the Panamanian Supreme Court could decide on the shah's extradition in less than a month, informed sources here suggested "perhaps the commission should drag out its hearings or at least delay publication of its findings."

Although the commission's terms of reference are apparently purposely vague, Khomeini said it would be "investigating past U.S. interference in Iran's internal affairs through the bloodletting shah's regime." He added that "the crimes of the U.S. and the shah will be proved."

Analysts long have predicted that any solution to the hostage crisis necessarily must be perceived in Iranian eyes as a victory for Khomeini.

Thanks largely to the Soviet invasion of Afghanistan, which scared the Iranian authorities and helped distract U.S. public opinion as well, the United States has found it expedient to accept conditions that it rejected in the first two months of the crisis with Tehran.

After first insisting Iran release the hostages without any conditions, the United States accepted the principles of a commission first suggested by Waldheim two weeks after the embassy's seizure.

The United States gradually dropped its insistence that the hostages be released before the commission began its work.

Even before Khomeini's statement today, the United States at best apparently was hoping for the token release of a few hostages during the commission's stay in Iran, but with the bulk to be freed after their departure.

Also abandoned since the Afghanistan invasion were U.S. plans to persuade Japan and Western Europe to apply economic sanctions against Iran. p

The U.S. allies argued that such sanctions would only drive Iran further toward the Soviet Union and accelerate the country's economic decline, which would benefit Iranian leftists.

Similarly, the U.S. Naval Task Force, which began assembling in the Arabian Sea in late November and early December as an example of otherwise frustrated U.S. determination in its showdown with Iran, is positioned there because of the U.S.-Soviet tension stemming from Afghanistan.

Whatever observers assume was negotiated in great detail between the Unites States and Iran before the commission was announced, the problem remains that Washington cannot afford to go too far to accommodate Iran's desire to apologize for alleged past misdeeds.

To do so analysts argue, would be to lay the Unites States -- and for that matter any government anywhere -- open to furtherseizures of embassies and Bani-Sadr publicly conceded recently were neither legal nor internationally acceptable, even if politically understandable.