Cold as it was last night ouside the Kennedy Center, the heat was kept low inside in line with the Carter administration's austerity policy and there was something chilling about the atmosphere in the Atrium of the roof terrace.

Quite a few of the 1,100 guests at a buffet reception after the premiere of a Robert Aldrich film, "Twilight's Last Gleaming," sported fur coats and fairly shivered at the thought of what they had just seen.

According to the program, "Twilight" is "a tense psychological drama involving nuclear blackmail and the question of U.S. foreign policy and the American public's right to know.

Sen. Charles Percy (R-Ill.) called the movie "startling" but wouldn't comment further except to say "a lot of people who hated the Vietnam war will like it." His wife, who accompanied him on a recent visit to Montana where they made their first visit to nuclear silos, said she thought the movie's technical details "very authentic" but that the film reminded her of "a TV thriller."

Sen. George McGovern (D-S.D.) said he felt "a little numbed" by the "remarkable" film, and that although he felt its impact should be "thought over for at least 24 hours" he was under the impression that "Twilight" could be "the most important film ever made," because it has "the potential for making the American government come clean about Vietnam." The American people still son't know what really happened, he said, and he had no idea how they would react to "Twilight" "except that anytime you touch Vietnam you make people angry."

Evangeline Bruce, wife of Ambassador David Bruce, wife of Ambassador David Bruce, and her escort Lord Chalfont - who said he had just flown in from London - found the film "very impresive, technically," although, Chalfont added, "I hope the United States never has a President like that one."

Asked what she thought of Rosalynn Carter as an American ambassadress, the legant Mrs. Bruce replied that she didn't think "we could have a better representative of our country's style."

The guests, including several ambassadors, Teamsters president Frank Fitzsimmons, Redskins player Larry Brown and such ubiquitous partygoers as Steve Martindale and Page Lee Hufty, tried to make themselves heard over the powerful sound of an oldtime swing band. Some clamored for autographs from Burt Lancaster, Richard Widmark and the rest of the cast.

Stewart Mott, New York philanthropist and McGovern contributor, evasive as always, said he had been in town this week of "meetings" and that he loved the film, "loved the message," but he refused to elaborate.

Rep. John Brademas, accompanied by Mary Ellen Bridges, a Georgetown medical student, said he felt that the point of the film - the need for credibility in government - was nearly defeated by the incredibility of the script, in which for instance the director of the CIA "practically told the President that there was such a thing as World War II."

"It needs editing," Brademas said. "It underestimates the intelligence of the American public . . . If Richard Nixon were alive today he'd say it was degrading to the United States, but I think we're strong enough to take it."