Two International Red Cross representatives visited the occupied U.S. Embassy here today under restrictions not normally accepted by the Red Cross and insisted later that they were sure they had seen all the American hostages.

"I will just tell you that I saw all of the hostages, that it took eight hours and that I'm rather tired," said Harold Schmid de Grueneck, a Swiss who is the permanent representative in Tehran of the Geneva-based International Committee of the Red Cross.

De Grueneck refused to say how many hostages had been seen, apparently as part of an agreement with the captors designed to pave the way for possible future visits.

If the Red Cross officials were allowed to see all the hostages, the visit today would be the first time that independent foreign observers have seen all of them since the embassy was seized Nov. 4.

Since neither the Red Cross officials nor the captors would say how many hostages were seen, however, a question still remains as to how many Americans are being held hostage and whether all those believed being held are accounted for. The State Department has said it believes 50 are being held.

State Department spokesman Hodding Carter said in Washington that if the Red Cross representatives saw all 50 Americans and were able to report on their status to their families, "it will be a plus," the Associated Press reported.

[But, he added, "it will be anything but a palliative, . . . a mask for the central reality that they are being held. Our objective is their release."]

De Grueneck and Bernard Liebeskind, a Red Cross doctor who flew here from Geneva for the visit, went to the embassy after they agreed to drop a customary Red Cross condition that detainees be interviewed privately with no other observers present.

"There were people around," De Grueneck said. "We could not have interviews without witness. But we were allowed to see all of the hostages." The Red Cross officials said at least one or two of the Moslem captors had been present during all the interviews.

De Grueneck said the team took messages from the captives and that these would be delivered to their families by the end of the week.

The Red Cross officials were vague about how they knew they had seen all the hostages and about where the interviews took place.

Pressed on the question, De Grueneck said, "I've seen all of them, according to the students." He added, "I have a firm belief that I have seen all of the hostages."

While giving no names, De Grueneck did say he had visited one of the few hostages who had not been seen or heard from before and reported that he was healthy.

Diplomatic sources had said earlier that they hoped the visit would clear up a mystery about the fate of Michael J. Metrinko, who has been unaccounted for, and hostages denounced by their captors as "spies" and believed held up in solitary confinement . Among these were said to be William J. Daugherty, Malcolm K. Kalp and Thomas L. Ahern Jr.

Metrinko, an embassy political officer and former consul in the northwestern Iranian city of Tabriz, was the only captive who had not been reported seen by neutral outsiders or who had not been heard from by his family since the embassy seizure.

De Grueneck said that for the past five months the hostages have been under "very heavy psychological conditions. So of course, they are not 100 percent. But I saw fit people to whom I could talk normally."

Liebeskind said the physical and mental conditions of the hostages were "not bad" and that he found only "minor problems" among them. He said they had regular access to medical attention.

The Red Cross officials refused to give further details of the hostages' conditions and would not discuss reports that some of the captives were suffering from depression.

Normally the Red Cross insists that in all visits to prisoners, the subject be seen in his usual place of detention, be interviewed with no other person present and be allowed to fill out a Red Cross questionnaire in complete privacy.

Informed sources said the Red Cross justified softening its terms by saying that the embassy hostages constitue a special category and that the normal Red Cross regulations governing visits to prisoners of war and other political prisoners thus did not apply.

De Grueneck said he had not consuited with the U.S. government before the visit on the conditions for seeing the hostages.

I took this decision along," he said, but he said he felt the hostages talked freely despite the presence of monitoring captors.

"It was not a visit which was done under strict ICRC conditions," he added. "We nevertheless accepted to do it because we do believe that what we could do was very useful for the families -- and we only think of the families -- in the States. As far as conditions of detention are concerned, a report will be done, and I will have some further talks with the students in order to improve what has to be improved."

He added, "I do hope to be able and allowed to make regular visits. Of course, I have no commitment from their [the students] side as far as regular visits are concerned. But they did seem receptive."

There was some question in diplomatic circles on whether the relaxation of Red Cross terms was a good move.

"I'm amazed," said one European diplomat. "Perhaps the face that the students have given in on at least some things is a development, but it just is not good enough. The EEC countries are deluded that this actually means something, but it doesn't. He conceded, however, that seeing all the hostages was important for Washington.

The Red Cross officials entered the embassy shortly after 1:00 p.m. Monday and emerged shortly after 10:00 p.m. After seeing the hostages, the officials were interviewed by Iranian news media before coming out of the embassy compound.

Also visiting the embassy Monday on the invitation of the militants were Iran's health minister, Dr. Musa Zargar; Tehran's Friday prayers leader, Hojatoleslam Mohammed Ali Khamenehi; and a doctor of the Red Lion and Sun Society, Iran's equivalent of the Red Cross.

Meanwhile, four ambassadors of European Common Market countries left for their capitals Monday, following a collective Common Market decision to recall envoys to protest lack of progress in resolving the hostage issue. The envoys of four other Common Market countries represented here, plus Japan, are to depart this week.

In another development late Monday night, one of the American hostages, believed to be political officer John W. Limbert Jr., 37, was shown on Iranian television being visited by Khamenehi.

There was no indication when the meeting was filmed, Iranian television has been broadcastingf interviews with Americans in recent days, some of whom described purported U.S. intelligence-gathering activities.

Limbert, who speaks fluent Persian, was shown having a conversation in that language with the Iranian clergyman in which he said he thought the deposed shah was "a criminal" and that he had "no objection" to the shah's return to Iran for trial.

Asked about the conditions of his detention, Limbert said, "It is good. What can we do? We have to accept it."

The American said the only problem was the hostages' continued detention and he joked politely with the clergyman that the students were being overly courteous in keeping their guests overtime.

Khamenehi said, "The students and the people of Iran want you to go home as soon as possible, but the key for this is not in their hands." He added that the release depended on the return of the dethroned shah.

The clergyman concluded, "I hope you will have good memories from them [the students]. Our brothers here in the embassy have humanitarian aims and intentions."