While news film of some of the 52 American hostages in Iran flickered on television screens across the United States yesterday, the Carter administration sought to throw a cautionary shadow over the visual evidence that the captives are being kept in comfort, if not in luxury as Iranian officials claim.

The film showed bowls overflowing with fresh fruit, a Christmas tree decorated with a large yellow bow, and hostages seated in comfortable chairs as they sent holiday greetings to their families.

The State Department had said Monday that it had reports, contrary to Iranians' claims, that some of the hostages were in prison and some were not receiving proper medical treatment.

It backed away from that assessment slightly yesterday, acknowledging that the visits of Algerian diplomats and the films indicated that the hostages are "apparently in good condition."

But in a statement the department added that "The concerns we expressed earlier about the conditions in which some of the hostages may have been held and about the possible lack of adequate medical attention . . . will obviously continue to apply" unless the film released. Thursday and yesterday "represents a permanent change" in the hostages' treatment.

President Carter, in an impromptu news conference in Plains, Ga., where he and his family spent the Christmas holiday, said he was "pleased" that all 52 of the hostages had been seen by Algerian diplomats. But he added: "It's still insulting to us to see them being held. . . . They are not free. That's the most important thing."

Carter made his statements after seeing a 4 1/2-minute videotape of 15 hostages with Iranian clergy and Msgr. Anibale Bugnini, the papal envoy to Iran.

President-elect Ronald Reagan, who had angrily denounced the Iranian captors as "nothing better than criminals and kidnapers," watched parts of the film footage yesterday, but had no immediate comment on it, a press spokesman said.

Families of the hostages, for the most part, found little in the films to raise their holiday spirits.

Hostage Kathryn Koob appeared on the film, singing a Christmas carol, telling her family that she reads and stays busy and has lost weight but is happy about it. Her mother, Elsie Koob of Jessup, Iowa, said she was encouraged but it was still hard to celebrate.

Betty Kirtley of Little Rock, mother of hostage Marine Cpl. Steven Kirtley, found the film unfulfilling.

"The feeling is bittersweet," she said. "We saw the film clip, but it was not like touching Steven. It was nice seeing him, but it was upsetting not being able to touch him, to talk to him."

And the mother of Marine Sgt. Johnny McKeel said in Balch Springs, Tex., that "The first time I saw him, I got a little bit angry. My blood started boiling. When I started thinking that he's over there for Christmas and everyone else is here, and he never did anything. . . ."

Her frustration echoed Reagan's, whose voice had risen in anger Christmas Eve as he talked of the hostages' captors "who have violated international law totally in taking these innocent people and holding them this long."

Carter, too, denounced the "criminal act" that has resulted in 14 months of confinement for the American hostages. But the president, who had expressed deep disappointment Wednesday over the prospects for an early hostage release, found some encouragement in the latest confirmation that all the Americans are accounted for and appear to be in relatively good condition.

"That's encouraging to me," Carter said, "because there were three or four we had not had confirmed as being well since last April, and now if this report is true -- and I believe it to be true -- then that is reassuring to know that they are all alive and well."

Carter said, however, that the conditions under which the hostages have been living are "not luxury," contrary to assertions by some Iranian officials.

"It's still imprisonment," he said. "It's a criminal act, has been from the very beginning," 14 months ago, when the U.S. Embassy was seized and the Americans taken captive.

The visit to the hostages by Abdelkarim Gheraieb, Algerian ambassador to Iran, and Mohammad Bel Hossein, an Algerian foreign ministry official, was the first by outside diplomats in eight months. The State Department noted that in its statement yesterday, saying it was pleased that the visit "which we have constantly called for has finally taken place" and expressing the hope that it will "set a precedent for regular visits by qualified outside observers."

Carter said in Plains that "it is now known" where all the hostages are being kept "at least at one time this week, and we believe they were observed where they are staying." Later, as he was leaving to finish his Christmas holiday at the presidential retreat at Camp David, he was asked where the hostages were being kept. "I can't talk about that," he replied.

For several months, the hostages' location inside the American embassy in Tehran was well known. But after the administration's abortive rescue attempt in April, the Iranians announced that they were moving the hostages to several undisclosed locations.

In the waning days of his presidency, Carter administration efforts to negotiate the hostages' release have faltered with new Iranian monetary demands. Carter has characterized the latest Iranian demands as "ransom" and unacceptable to the United States.

"We'll continue to protect our nation's honor, to work for the hostages' release and to make sure that we do everything we can to protect them from any abuse and to make sure they stay alive and well," Carter said.

"We'll continue to, as best we can, to [try to] acquire their freedom," he said, "but we just don't know what the future will hold."

In Krakow, Mo., the parents of hostage Marine Sgt. Rodney Sickmann voiced the same sense of helplessness.

"It's a never-ending thing," said Virgil Sickmann. "We wonder, could it be spring, could it be summer, could it be another Christmas before he comes home?"