Special envoys from a number of foreign governments, apparently acting at the request of President Carter, have been dispatched to Iran to press for the release of the American hostages being held inside the U.S. Embassy there, State Department officials confirmed last night.

The envoys, believed to number at least three, with possible others to follow, represent both European and Middle Eastern governments sympathetic to the U.S. position in the five-week-long Iranian crisis.

The special missions appeared to have been undertaken at the direct request of the U.S. government. A State Department official said last night that the administration has been aware of the envoys' plans for several days.

He said the foreign envoys did not carry specific instructions from the U.S. government, but were prepared to press in private for the same demands the United States has been making in public for more than a month.

This, the official said, amounts to a demand that the hostages be freed immediately, coupled with a U.S. promise to participate later in an international forum at which Iranian authorities could air their grievances against the deposed shah and the United States.

From the outset of the crisis on Nov. 4, the U.S. case has been carried to Iranian authorities through sympathetic foreign governments with diplomatic personnel stationed in Tehran. The dispatch of high-ranking envoys from the capitals of other nations was clearly calculated to increase the diplomatic pressure being brought to bear on Iran.

"There is a full-court diplomatic press, and this is part of it," the State Department official said. He said other measures will follow.

Dominating the outlook for the next phase of the long-running crisis was the growing likelihood that the hostages would be placed on trial for espionage, despite public and private U.S. warnings that this act would have grave consequences.

Much of the discussion and contingency planning in the top rank of American officialdom revolves around the prospect and problem of spy trials, which would be deeply offensive to the American public.

The unannounced agenda of Secretary of State Cyrus R. Vance's whirlwind trip to London, Paris, Rome, and Bonn, which begins tonight, is to line up support of the European allies and of Japan -- whose foreign minister Vance will see in Paris -- for financial and economic measures to be taken against Iran in response to trials of the American diplomatic personnel.

"If the hostages are tried, we would take steps to interrupt commerce with Iran," Carter told family members of the hostages Friday in remarks meant to be confidential but which were made available by one of the participants to The New York Times. Carter was quoted as adding that such action to "interrupt commerce" might restrain or cause problems for Iran "but wouldn't lead to bloodshed."

In a White House breakfast yesterday for broadcast journalists, the president expressed the view that Iran is already feeling an economic squeeze arising from U.S. seizure of Iranian assets, a sharp increase in international insurance rates on shipments there and the refusal of American longshoremen to load goods destined for that country.

Carter's analysis, which could not be attributed directly to him under the ground rules of the "background" breakfast, was that Iran has suffered a decline of imports ranging between 65 and 80 percent.

The hostages' families reportedly were told by Assistant Secretary of State Harold H. Saunders that "the people who make decisions in Iran have to realize that nothing more is coming from the United States and [that they] can look forward to shortages in January and Februray," especially of food.

The potential cutoff of supplies, spare parts and capital investments by America's allies would be an even more serious matter for Iran, in the view of Washington policymakers.

On the other hand, there is little confidence that either the current squeeze or future international economic restrictions can stave off the convening of spy trials. The predominant signals form Tehran and Qom, in fact, run the other way.

The greatest uncertainty at the moment is not whether trials will be held but how they will be held, who will be involved and what their purpose will be. Among the unanswered questions are:

Will the Americans be tried by the "student" militants holding the embassy, by an Islamic court or by the tribunal of "independent freedom fighters" suggested yesterday by Foreign Minister Sadegh Ghotbzadeh?

Will all of the 50 American hostages be tried or will some be released soon and the rest tried, as Ghotbzadeh declared and as their captors denied? There have been reports than a small number of the hostages, perhaps eight or so, have been singled out for particularly intensive questioning in the student belief that they are the real "spies."

Most fundamental and important, are the trials and the newly announced tribunal an Iranian way of seeking a face-saving way out of the crisis with the United States, or are they a way of prolonging and even intensifying the conflict? The United States is seeking an answer to this question above all.

If the trials are a way out, some or all of the Americans could be taken to court, found guilty and expelled. Another and equally likely scenario, though, is that some of the "guilty" diplomats would be expelled and some might even be found innocent -- but a small group would be imprisoned and thus be hostages over a long period of time until and unless a deal were made for their release.

It seems unlikely at this point that any of the hostages would be executed, given the worldwide condemnation, and U.S. retaliation this would bring about.

The United States has ground for believing that some members of Iran's Revolutionary Council, perhaps even a majority of the members, would like to find a way to settle the conflict with the United States. But there is no indication that this view is shared by the militants holding the hostages. And the mindset of Ayatollah Ruhollah Khomeini, the most important part of the hydra-headed authority in Iran, is unknown beyond his hardline rhetoric.

In earlier assessments, the week now ending had been looked upon as the time when a resolution of the crisis might begin to come into view. The deposed shah was to have left the United States for Mexico. The constitutional referendum in Iran was to have strenghtened Khomeini's hand so that he would have both the incentive and the means to get on with a settlement of the crisis. The United Nations Security Council resolution was to have strenghtened U.S. and international pressures for a settlement.

As often has been the case since the embassy and the hostages were seized five weeks ago today, the reality departed wildly from the expectation.

Because of Mexico's sudden refusal to accept the return of the shah, an act which has generated bitterness in the White House, the United States at the moment has greater and more direct responsibility for the deposed monarch than before.

The former shah's stay at Lackland Air Force Base in Texas is expected to be temporary. U.S. officials calculate that, on balance, it would be better for him to leave this country than to stay, from the standpoint of the future of the hostages. Carter, in his breakfast with the broadcast reporters, expressed great confidence that a new home for the shah will be found.

The internal situation in Iran, far from being clearer, is more uncertain today than before. The open conflict between Khomeini and his rival, Ayatollah Kazem Shariatmadari, which developed in recent days, is a new element of potentially great importance but of unknown effect.

The revolt in the Azerbaijan region and the threat of revolt by other national minorities could induce Khomeini to settle the hostage crisis to get on with more important national business -- or it could seem to him to call for keeping the hostages and maintaining the fierce anti-American campaign as a unifying national cause.

It is increasingly evident that the Iranian government's influence over the militants holding the U.S. Embassy is shaky, and it is not at all clear that even Khomeini has full control over them.

The U.S. government first learned from the "students," in one of the remarkable daily telephone conversations form the State Department in Washington to the occupiers of its embassy and captors of its diplomats in Tehran, that the hostages were to be placed on trial. The original suggestion was that the trials might be quickly convened. This is one reason why the White House reacted to the prospect of trials so sharply and promptly on Nov. 20, two days after Khomeini himself first spoke of them in answer to questions form American television interviewers.

There are signs that the "students" in the embassy, far from deferring to Khomeini, aspire to the lead role in any negotiations over the fate of the hostages and in any trials which are to be held. There is suggestive evidence that the seizure of the embassy itself was the idea of a few militant university students, perhaps as few as a dozen, and approved by Khomeini after the fact, when he had little choice about the matter.

As the days have gone on, the identity and operations of the embassy captors have come slowly into better focus. The initial group of highly religious, pro-Khomeini militants who took over the embassy appears to have been joined by revolutionary Marxist elements with a more secular orientation. The top layer, in overall charge, appears to be a leadership group predominantly in its 30s, whose main point of contact with outside authority is the ayatollah's son, Ahmad.

The imam may be riding a tiger rather than directing one from afar. The "students" are issuing daily policy pronouncements and conducting daily telephone conversations with Washington. They are bidding to be the judges in the trials. Beginning with talks at the embassy yesterday with two University of Kansas professors, the "students" may be heading into negotiations with Americans. In some respects the embassy captors are acting more like a government than anyone else in Tehran.