Former president Jimmy Carter, after an emotional meeting with the released hostages, denounced Iran tonight for a "despicable act of savagery" and said the Americans' captors subjected them to previously undisclosed "acts of barbarism" that "can never be condoned."

Carter's suddenly strong language reflected 14 1/2 months of irritation built up as he sought to obtain release of the 52 captive Americans through threats, sanctions, negotiations and, at one point last April, a failed commando raid.

Breaking a self-imposed pattern of restraint on the issue, Carter's comments followed an 80-minute private visit with the returned hostages that an aide described as "emotional to the point of awkwardness."

Carter embraced the returned Americans one by one in a third-floor community room of the hospital here and tears frequently welled in his eyes, according to officials present. He was photographed with each of the returnees, they added.

After the meeting, Carter said he told the hostages that "Iran suffered severly" from its acts and that in the resolution of the long crisis "terrorism had been proved not to pay."

"This proves we could not be forced to pay ransom," he added. He paused, beginning to smile for the only time during the statement, and went on: "Because -- and they started to cheer when I said this -- out of the $12 billion in Iranian assets that I froze after they took the hostages, we are paying them only about $3 billion of thier own money."

The former president was accompanied by several members of his administration, including former vice president Walter Mondale, ex-secretary of state Edmund Muskie and former treasury secretary G. William Miller.

In his remarks shortly before departing, Carter said that West Germany Chancellor Helmut Schmidt and Foreign Minister Hans-Dietrich Genshcer had helped during the hostage crisis "in ways which I can never reveal to the world."

Carter, who came to West Germany at the request of President Reagan, flew back to the United Sates tonight.

Echoing the same theme as Carter and basing its assessment on interviews with the hostages, the U.S. State Deparment issued a statement here accusing Iran of "serious mistreatment in a number of cases" during the hostages' captivity.

Neither Carter nor the State Department cited any specific abuses to back up their charges. The State Department promised further reports" on the facts as they emerge" and added:

"The medical team at the Wiesbaden Air Force hospital has conducted preliminary conversations throughout the day with the 52 Americans who have been freed from Iran. We want to stress that this evaluation of thier experiences is preliminary in nature and that no comprehensive judgments can be made at this time."

Carter, speaking out for the first time as a private citizen with all of the hostages back safe in American hands, was less cautious. "Our Americans were mistreated much worse than has been previously revealed," he said. "The acts of barbarism which were perpetrated on our people by Iran can never be condoned."

Aides to the former president said some hostages were put in front of what they called "mock firing squads" as part of mental and physical torture during their imprisonment. Hamilton Jordan, Carter's former chief of staff, said Carter was "clearly outraged" by the hostages' account of how they had been treated by the Iranians who held them for 444 days.

The former hostages, celebrating their first full day of freedom in the West, slept or talked in what for many was the first opportunity to compare experiences during their ordeal.

While the reports filtered out of their sufferings, they stayed largely out of public sight within the white walls of the military hospital. Jack Cannon, a State Department spokesman, gave only one general account early in the day of the ex-captives' initial hours of regained freedom.

Much of the free hostages' time during their 12-hour flight to freedom from Iran via Greece and Algeria to Frankfurt this morning was spent getting to know each other again after being split up when taken hostage No. 4, 1979. "They were sharing experiences they had during the last 14 months," Cannon told reporters.

It is expected that an important part of the readjustment process for the former captives -- in addition to talks with families, friends and doctors -- will be sessions with each other in order to sort out, compare and orient their individual kidnaping experiences.

As soon as the Algerian 727 passenger jet that ferried them from Tehran to Algiers was airborne last night, Cannon said, "Everyone loosened their seatbelts and immediately rapped with each other in a great communal get-togetherness."

"It was, we are told, the first time during the entire time they were incarerated that they had been together," he added.

As they returned in to American hands, Cannon said, they also "were very intent on discussing what has been going on in the world," during the time they were cut off.

Indicating that as hostages they were still held in separate groups to the very end, Cannon said, "There was some indication that some of the people had very little notice at al" before being freed," perhaps 15 or 20 minutes," while others "had several days."

But Cannon was unable to elaborate on this. Nor could he give anything but imprecise answers to many other questions posed by an army of newsmen here regarding the behavior and history of the former hostages. a

"We've had very little time to talk to them," he said.

Once on the U.S. planes that brought them from Algiers to West Germany, the ex-captives celebrated with champagne and a turkey dinner, Cannon said, "and I understand that went down rather well."

When they checked into the Air Force hospital here just after dawn today, he said, "There was a very heavy run on the telephones" for calls to relatives and friends in the United States and then most of the freed hostages went to sleep. When they woke up later today, he said, the first of extensive medical and psychological examinations would begin.

He refused to answer questions about details of the examinations or scheduled debriefings of the former hostages by members of a 30-person State Department team flown here from Washington hours before the hostages arrived.

Cannon also was adamant that government officials had "no plans for press access to the hostages whatsoever" because of "our concern that this is a very private time for them to rest, undergo their physical exams and the like."

At the same time, he stated that as "free men and women" the former hostages could not be prevented from talking to the press if they chose to do so.

Despite complaints from reporters, Cannon said he would brief the press only once a day during the "several days" he expects the former captives to be here. He said later in the day, however, that the public might get additional government statements in reference to the ex-hostages on an ad hoc basis as the week unfolds.

This left the huge corps of correspondents, photographers and television technicians who have massed here standing on a cold sidewalk outside the hospital for much of today, peering over a high wooden fence for revealing signs of activity by the freed Americans, many of whom had donned blue pajamas in their rooms.

In demonstration of pleasure at being newly freed -- and as apparent evidence of restlessness and vigor -- several of the young Marine guards who had been held hostage stepped out onto hospital porch around noontime to chat casually for an hour and laugh with people in the courtyard three stories below.

Just beginning to adjust to their celebrity status, the Marines tossed out autographs scribbled on yellow ribbons or on copies of the Stars and Stripes newspaper.

The families of the ex-hostages appear to be honoring government wishes that they remain in the United States. At lease one freed American -- Donald Hohman, 33, a Marine Corps medic -- saw his wife, Anne, a German national who is a resident of Frankfurt.

Allyssa Keough, 19, daughter of former hostage William Keough Jr., tried to see her father after Carter's meeting with the hostages, but was told he was resting under the exhausting journey from Iran.

In answer to questions about the conditions of the freed hostages, Cannon said it was "premature" to speculate on their physical or mental health because intensive tests had not begun before he met with the press here today. He noted only the ex-captives looked well and that none required immediate medical treatment from the doctors and nurses aboard the specially equipped hospital planes.

A government psychiatrist who is a member of the team of physicians sent here by the State Department cautioned against uncritical acceptance of early expressions of relief and happiness by the former hostages.

He said these expressions were typical of captives at the moment of their release. But he said other more negative emotions -- including aggression, anger, frustration and confusion -- now masked by the excitement of the moment, could be expected to emerge during debriefings here and later after the hostages return home.