New accounts of bread-and-water diets, strippings, beatings and forced around-the-clock standing or sitting in shackles emerged today as the freed American hostages continued to tell government interviewers, doctors and relatives of their treatment during their captivity in Iran.

One of the former hostages reportedly was kept in solitary confinement for 374 of the 444 days he was held. Others told of guards spitting in the meager rations of food before serving them, burning unopened Christmas gifts and displaying letters from home but refusing to distribute them.

Even the U.S. embassy's charge d'affaires, Bruce Laingen, who was in the custody of the Iranian Foreign Ministry rather than militant students, said he had been kept in a darkened room much of the time and allowed to go to the toilet only three times a day.

State Department spokesman Jack Cannon said here today, "The evidence now is mounting from the discussions we are having, and it shows much worse and more extensive mistreatment than we previously had evidence of." m

A senior White House official who met with the freed hostages here said in Washington that, considering their treatment, it was "almost a miracle that all seemed to be in good condition physically."

[In Tehran, Behzad Nabavi, the chief Iranian negotiator in the hostage release, indignantly denied that the captives were maltreated, the official Pars news agency reported. Nabavi was quoted as saying Iran had videotaped interviews in which the hostages said they had been treated well and he said Iran might release the tapes to show "which is the hair, Washington or Tehran." Details on Page A9.]

Although Cannon refused to specify individual cases, the broad picture he presented paralleled and expanded on the stories of mistreatment the hostages' relatives have been passing along to the press, and a pattern of mistreatment that former president Jimmy Carter, after talking with the freed Americans yesterday, described as "unbelievable savagery."

The information being compiled from the freed hostages by psychiatrists and interviewers from "various government agencies," according to Cannon, depicts:

Poor food and primitive living conditions."At least several persons were on bread-and-water diets for at least two weeks," Cannon said. "Others were forced to eat stale commissary food, including wormy powdered milk" while their guards ate meat and vegetables.

"Some persons were manacled to single folding chairs for as much as 14 to 15 days around the clock," Cannon said, and others "were forced to stand in cold weather for long periods of time, including night, in poor clothing."

Imprisonment and solitary confinement. Some hostages were kept in actual prison cells, Cannon said, and others were kept in solitary confinement for months "in cell-like conditions in various other places."

Michael Metrinko, a political officer at the embassy, has said he spent nine months in solitary confinement. Relatives of Malcolm Kalp said he told them by telephone that he spent 374 days in solitary confinement. Col. Leland Holland, a military attache said he spent a month in a "dungeon."

Physical abuse. "There were a number of cases of beatings on a number of occasions" during the American' 14 1/2 months of captivity, Cannon said, but he say that "we have no reports so far sexual abuse."

Intimidation. "A number of persons were on several occasions threatened with loaded revolvers," Cannon said. Others were ordered by terrorists with loaded rifles "to strip off their clothes, and lie on the floor and were threatened with death. Many thought they were going to be executed."

Marine Sgt. William A. Gallegos and Richard Queen, the hostage who was released last year because of ill health, have said they were put before such mock firing squads. Another hostage released earlier, Lloyd Rawlins, said two embassy secretaries were forced to play Russian roulette.

Isolation. Besides the cases of solitary confinement, most of the hostages were segregated in small groups, blindfolded when moved from place to place and cut off from the outside world most of the time.

Mail was denied them for long periods and most of the letters they wrote never left the country. Economist Robert Blucher has said he was taunted with letters postmarked in his home town and addressed in his mother's handwriting.

Most of the hostages were ordered not to speak to each other, although some communicated by whispering or sending messages in code from room to room or cell to cell by tapping on the walls.

Air Force Capt. Carmelo Scalzi, a medical corpsman who traveled on the plane with the freed hostages from Algiers to Wiesbaden, told the Detroit Free Press in a copyrighted interview that "they told me some almost unbelievable tales about what it was like.

"They said they had bad food and no sunlight. They said they'd find nose hairs in the food and they'd see guards spit in the food just before they gave it to them.

Some of the hostages, including Gallegos, have said they were punished with worse deprivation after the abortive U.S. military rescue attempt last summer. But Cannon said most of the mistreatment seemed haphazard, except for punishment for several escape attempts by some of the hostages.

"Their treatment differed from time to time, place to place and person to person," Cannon said. Some "were guarded by persons who obviously were more severe in their treatment of the hostages. Some were treated a little better than others."

In Washington, the senior White House official who had met with the freed hostages in West Germany, also said that while the treatment they had received was "much worse than we thought," it had varied widely.

"Some were treated almost as guests throughout the period," the official said. "Some were treated badly at first and then much better. And some were treated badly over a long period of time."

With direct media access to the freed hostages largely denied here, this outline of what they have been telling interrogators appears to be part of a determined effort, begun by Carter, to emphasize their mistreatment by the Iranians.

Cannon referred to officials in Washington questions about possible implications of this for future relations with Iran or the carrying out of the U.S.-Iranian agreement that led to their release. He also would not answer questions about Iranian accusations that many of the former hostages had been spies in Tehran or whether any of their interrogators here are from the U.S. Central Intelligence Agency.

Barry Rosen, the former press attache at the American embassy in Tehran and one of the few former hostages to make direct contact with the press here, told reporters in a brief conversation at the entrance to the U.S. Air Force hospital that he thought the hostage release agreement with Iran "should be looked at, but that would take time."

"I feel Iran is an outlaw country," Rosen said, "and it deserves tremendous crisicism from the world for its treatment of the hostages."

United Press International reported from Wiesbaden:

Hospital personnel and visitors who saw the hostages said that while most were overjoyed, a few -- particularly the older ones -- were so depressed that they cried a lot and kept to themselves.

"There is one guy, and he acts very shy," said Margaret Blakeley, 18, a cashier at the Wiesbaden military hospital where the hostages are being examined. "He doesn't like to talk to people. He just walks down the hall with his head bowed."

Blakeley said the younger hostages, especially the Marines, appear to have adjusted well but that some of the older diplomats were having a difficult adjustment.

"Their eyes get red and they start watering, and they'll say 'Please give me some more time, I'm not ready to talk about it yet," she said.