Iran today launched a campaign to enlist the help of foreign governments in persuading the United States to hand over the exiled Shah Mohammad Reza Pahlavi.

Foreign Minister Abol Hassan Bani-Sadr announced here that he will summon foreign ambassadors in Tehran this week to ask them to support Iranian demands for the extradition of the shah -- now undergoing treatment for cancer in a New York hospital -- to his homeland to face an internationally attended trial.

Despite growing gloom about the prospects for the quick release of U.S. Embassy hostages who are starting their second week of captivity, the new Iranian campaign appeared to open the door -- if only slightly -- to an eventual way out of the crisis, according to independent observers.

[President Carter, meanwhile, called top advisers -- including Secretary of State Cyrus Vance and Energy Secretary Charles Duncan -- to the White House Sunday night to discuss the implications of the embassy takeover, the Associated Press reported.]

By taking its campaign into the international diplomatic arena, the outside observers noted, Iran was opening theoretically discreet channels that could, in due course, persuade the country's militant Moslem leaders to settle for something less than their hard-line demands.

Meanwhile, there are growing worries about the physical and mental well-being of the hostages, despite Bani-Sadr's promise to journalists today that the captive Americans would not be harmed even if the United States were to intervene militarily on their behalf.

Ayatollah Ruhollah Rhomeini, who received Papal Nuncio Annibale Bugnini yesterday in the holy city of Qom and who rejected a papal appeal for release of the hostages, permitted the nuncio to visit the Americans today.

Although Khomeini told him yesterday that "they are not uncomfortable at all," the visibly shaken papal envoy admitted to being "very moved" after his visit to the embassy today.

Some hostages, identifying themselves as Roman Catholics, fell on their knees and asked for benediction. Bishop Bugnini reported that the hostages seemed "morally tired" although "their physical condition did not seem too bad."

Asked if he had been able to discover if 33 of the hostages whose names appeared on a demand asking for the shah's repatriation actually had signed the document, he said, "I asked three or four people if they had been obliged to sign and they told me clearly no."

Following four foreign diplomats' visit to the hostages Saturday, diplomatic sources reported that the hostages have not seen the sun since their incarceration began because the blinds are drawn in the rooms they occupy in various buildings in the embassy compound.

In another development today, the newspaper Etelaat reported that Red Cross representatives had visited L. Bruce Laingen, the American charge d'affaires who is still said to be detained at the Foreign Ministry. No Revolutionary Guards were visible at the ministry today, raising the possibility that he has been transferred elsewhere.

The students at the embassy today released another purported American document, this one allegedly showing American covert aid in helping the shah's Navy commander, Adm. Kamal Habibollahi, escape from Iran in July.

Khomeini signaled the start of the campaign in the international community yesterday during his audience with Bugnini.

In turning down the request, Khomeini suggested that Pope John Paul II "get in touch with Carter, who had appealed to him and to send some people to study the case."

"If the pope really decides" that all the shah's alleged crimes were not proven -- if he would say the hostages "should be let free," without the shah being put on trial -- then "the pope should say so," Khomeini said.

Bani-Sadr's announcement today followed Khomeini's and his own message yesterday to the American people designed to force Carter to hand over the shah.

He also announced plans to put the deposed monarch on trial in a kind of modern-day version of the Nuremberg war crime trials of Nazi leaders organized by the Allies after World War II.

"We want a trial to defend the dignity of the Iranian people, and raise their morale to overcome obstacles and reconstruct the country, Bani-Sadr said.

The immediate prospects of any movement toward releasing the 60 to 65 Americans in captivity, however, seem dim.

As one veteran diplomat remarked, "Khomeini intends to extract a high price from the United States when he eventually decides to start talking turkey."

Ticking off the now rejected initiatives by the European Common Market ambassadors, Bugnini and the Palestine Liberation Organization, another diplomat said, "So many things produced nothing. It's very disappointing. None of these approaches made a dent in Khomeini's armor."

PLO negotiator Abu Walid, who conferred with Bani-Sadr yesterday, flew black to Beirut today to report to PLO leder Yasser Arafat on a mission that shows every surface sign of failure.

Palestinian sources said, "We need a clear-cut mandate from both sides -- at least one side should know what it wants."

The sources felt, however, that the PLO had picked up some credit in the United States for its honest brokering.

"At least Americans will see the human face of the Palestine revolution," one source said, noting that the Palestinians, too, had been asked to carry Iran's brief for extredition to the United States.

One reason for gloom about the prospects for any rapid developments is that Khomeini, who openly supported the radical students only two days after they took over the embassy, does not want to be seen climbing down from his uncompromising stand without a decent interval elapsing, according to analysts.

The students say they are acting according to Khomeini's "mind." The ayatollah says the problem is one for the entire Iranian nation, and his advisers insist he is not intervening because he "is not a dictator."

That all adds up to a situation in which Khomeini needs time to let tempers cool even as he stokes the campaign against the United States -- he denounced the United States today again as the "great Satan" and called Presient Carter an enemy of mankind -- or weighs problems having nothing directly to do with the hostages.

Eventually, he might release the hostages, analysts said, in exchange for a combination of gestures ranging from perhaps severing diplomatic relations, or admission of what is regarded here as past U.S. guilt in its dealing with Iran, to having the shah leave the United States for another country or officially repudiating American recognition of the Pahlavi family's rule.

In confirming the meeting of Carter and top aides, deputy White House press secretary Patricia Bario refused to say what subjects were discussed or what conclusions may have been reached, the AP reported.

Bario called the meeting "another assessment of the situation and what is possible that can be done."

After the dinner-hour meeting, Vance continued talks at the State Department with officials from Energy, Commerce and Treasury departments.

[Duncan's presence at the session indicated that energy was on the agenda. The United States imports about 500,000 barrels of oil daily from Iran. Bario told the AP that "no dramatic incident" prompted the unnanounced meeting and that there did not appear to be a threat of an oil cutoff from Iran.]