The five-man U.N. commission charged with hearing Iran's grievances against the deposed shah, Mohammad Reza Pahlavi, today received the green light to leave Saturday for Tehran to begin a fact-finding mission that could lead to the release of the estimated 50 American hostages there.

Despite a still unexplained three-day delay in their departure, the public comments by the commission members were optimistic.

"We feel, as we have felt from the very beginning, that there is good to be done and we're going to do it," Andres Aguilar, former Venezuelan ambassador to the United States, told reporters at the European headquarters of the United Nations.

Despite the high hopes of the U.N. officials, there is no known formal guarantee that the release of the hostages would be linked directly to the fact-finding mission.

At U.N. headquarters in New York, commission chairman Mohammed Bedjaoui of Algeria met with U.N. Secretary General Kurt Waldheim before flying to Geneva to join other panel members for the noon departure Saturday.

"There are no problems.All is all right," he told reporters.

U.N. spokesmen said the go-headed came to U.N. headquarters in New York and Geneva early in the morning in an "official communication from the Iranian Foreign Ministry."

[One U.N. official said, "Things are developing normally, the secretary general is satisfied with the situation at present . . . everything is on track, any other speculation is unfounded."]

In Tehran, meanwhile, Iranian President Abol Hassan Bani-Sadr said in a speech that maintaining law and order was the most important problem facing his revolutionary government.

He blamed Revolutionary Guards for provoking some of the clashes in northern provinces and vowed that no mercy would be shown to those who disturbed the peace.

The official explanation for the three-day delay in the departure of the U.N. commission for Iran was said to have been that the Iranian government needed additional time to make physical arrangements for the panel. There were suggestions, however, that Iran possibly had posed last-minute conditions unacceptable to either Waldheim or the U.S. government.

Indicative of the official eagerness discernible today was the Venezuelan's suggestion that the commission start its work on Sunday, which in Iran is a work day. A chartered Swiss airliner was standing by at Geneva's Cointrin Airport for the noon takeoff.

However, informed sources close to the International Commission of Jurists were having doubts about the wisdom of sending the U.N. commission to Tehran without the existence of ironclad guarantees that the American hostages would be released.

The Venezuelan, Sri Lankan Hector Jayewardene and Frenchman Louis Pettiti are all either members or associates of the Geneva-based ICJ, which was instrumental in putting together the five-man team.

So serious did they regard their misgivings that the ICJ privately was said to have favored delaying the mission's departure until Iranian authorities came up with the desired guarantees.

Whether or not Iran has done so was not immediately clear.

Among the fears expressed privately was the off chance that documents and testimony provided for the fact-finding commission -- especially concerning torture, arbitrary arrests and other excesses -- could somehow be used to lead weight to Iran's demand for the shah's extradition or even the continued detention of the hostages.

Informed sources said that the two professional diplomats on the commission -- Bedjaoui, the Algerian ambassador to the United Nations, and Adib Daoudi, foreign affairs adviser to Syrian President Hafez Assad -- were less worried about such legal niceties.

Bedjaoui, who returned to New York after the commission's departure from Geneva was delayed Wednesday, said then that a "gentleman's agreement" existed involving the hostages' release.

Lawyers close to the Iranian government doubted any formal guarantees existed and they worried about the possibility that Ayatollah Ruhollah Khomeini might yet veto the hostages' release.

But the lawyers reasoned that the commission members enjoyed sufficient prestige to dissuade even Khomeini from compromising the mission or subjecting its members to the kind of humiliations meted out to Waldheim in Tehran during his early January visit to Tehran.

"After all none of them kissed Princess Ashraf's hand," one lawyer said, referring to the photograph of Waldheim with the shah's twin sister that appeared in Tehran newspapers at the time and enraged Tehran crowds.

Meanwhile, informed sources here suggested that the Geneva-based International Committee of the Red Cross might at some point take formal charge of the hostages in a transition phase between their release from the captors at the embassy and their eventual departure from Iran.

News services also reported these developments regarding Iran:

In Panama, the government of President Aristides Royo has let it be known it may not accept the findings of the U.N. commission. An editorial in the daily Matutino, believed to reflect government opionion, said, "The findings are not a mandatory order that Panama must carry out."

The newspaper said the Panamanian administration does not intend "to proclaim the innocence or guilt of the former Iranian monarch."

Bani-Sadr's warnings of harsh treatment for rioters came as gangs of Moslem fundamentalists wielding knives, clubs and stones attacked supporters of the radical Islamic Mujaheddin guerrilla movement in southwest Shiraz and the northern towns of Qaem Shadr and Gorgan, near the Caspian Sea.

Revolutionary Guards in Qaem Shadr told the Reuter news agency by telephone that an estimated 500 people had been injured in two days of clashes in the city. More detailed casualty figures were not immediately available.