The night was record cold, but 20 teen-age bodybuilders braved it in bluejeans so they could see their idol get out of a limousine and walk into a move theater. They greeted him with frantic chants of "ARR-nod, ARR-nold," and these shouts became visible puffs of gray in the hard night air.

Arnold Schwarzenegger smiled and waved to them but hurried inside, past police barricades and into an adoring hornet's nest of popping flashbulbs. This was not to be a night for Arnold's old constituency. This was to be a night for his new one. He had moved uptown, to be among the rich and pretty, the people called beautiful. About 500 of them turned out to see Arnold in his new movie, "Pumping Iron" and to sample the thrills of biceps chic.

James Taylor and Carly Simon were there, and so were Tom Wolfe, Paul Simon, Anthony Perkins, and oodles of oglers. This invitational premiere was part of gambit to promote the film by proving it is truly in. Thus has Schwarzenegger been hustling his cartoon-hero smile and his 57-inch chest all over the glamour stratum of New Yawk, a tour that last week took him to the literary spa known as Elaine's and a meeting with Jacqualine Onassis.

"She likes very much where I came from," Schwarzenegger recalled later. He comes from Graz, Austria. And no, Jackie didn't try to squeeze him. Others have been unable to show such restraint. Social columnist Liz Smith was all giggly in The Daily News over a luncheon at which she and Arnold exchanged pinchie winchies. "It was one of my proudest moments in journalism," she wrote.

"The girls, they always want to touch you, and they say, 'Arnold, take your clothes off' and so on," said Schwarzenegger. "I like that, because you get attention. But they always think you are getting to be rock hard all of the time. Barbara Walters felt my arm and said. 'My God, it's soft!' What they feel is like everybody else's body - only just a little bit bigger."

Arnold's biceps terms, fame is not that new to Schwarzenegger, but only in the past few years has he gone from the smaller limelight of sideshow bodybuilding to the media-sanctioned, special-celebrity status of culture hero. He brough some of the limelight with him, partly through the 1974 book version of "Pumping Iron" and partly by proving that muscleman isn't necessarily a fathead.

Now the former Mr. America and Mr. Universe and Mr. Everything is one of those singular stars whose devotion to a peculiar lifestyle finally paid off in rewards greater than the kind one gets from his own peer group. Charm is largely responsible here: Schwarzenegger has madea running joke of his half-mock-conceitedness and requited love of self. He describes his overdeveloped and outlandish megabody as "perfect."

He is neither fazed nor fearful of being the latest freaky cult item for the leisure set either. "I have always been accepted in high social classes," he says in his near-Viennese accent.

Schwarzenegger entered the Plaza Theater premiere to a volley of kisses from pretty girls penetrating a sea of faces that was polkadotted with Paradise Island tans and rubbing many an elbow adorned in too-too fake fur. Outside, the freezing loyal fans were shouting. "Come back out here. Arnold." And Arnold didn't seem to hear them. He was busy giving a big hug to columnist Earl Wilson.

"I pulled every string in town to get these tickets!" bragged a tuxedo'd man to his friends. But to some, the allure of all this was on the mild side. Laraine Newman, one of the bright young stars of "NBC's Saturday Night," only came because producer Lorne Michaels had given her his ticket. "If it's not good. I'm going to leave," she promised herself.

She was asked why so many chic folks seemed so excited about this new phenomenon. "Oh, they're probably BORED," she said.

"Ugh! All these ghastly people showing up for muscles!" tsk-tsked Mary Guettel, daughter of Richard Rodgers. But movie distributor Don Rugoff, whose Cinema 5 came to the rescue with the money needed to finish thepicture when the producers ran dry, looked pleased by the anxious crowd guzzling wine as it awaited the film.

"You know, Arnold posed at The Whitney Museum last yar, and 2,500 people showed up," Rugoff said. He could not explain why bodybuilding had suddenly became so interesting to such smart, smart people. Does the subject interest Rugoff? Without one instant of hesitation, he said, "No."

Then he notices that his "no" had been recorded in a reporter's notebook. "If you put that in the paper, I'll send three of these muscleboys down to get you," he said.

Surely he was kidding. Besides Schwarzenegger seems so essentially harmless. (He says he cried when he saw "A Star is Born.") At the premiere, Schwarzenegger beamed in a tuxedo that had to be made to order when a tour of rental shops proved fruitless. After the movie, he stood up in front of the crowd and handed out credit to everybody else connected with the picture, even though he is not only its star but its reason for being. Then he introduced five bodybuilders who proceeded to flex and twist and make mean faces to music.

The climax of this little vaudeville show was unexpected though hardly unlikely. "There 's a famous, famous star here." Schwarzenegger announced. "Carroll Baker!" Not-all-that-famous Baker raced up to the stage as fast as a slinky dress would let her. "This woman is going to touch everyone," Schwarzenegger announced. "Feel Big Lou's thighs," he coaxed her. Baker complied, flitting among the five near-naked musclemen, then pretending to faint with ecstasy, and right into the arms of Schwarzenegger, too.

No on seemed to think the scene unusually decadent - reminiscent of, says, Eugene O'Neill's "The Hairy Ape" (though most bodybuilders parade around hairless and oiled), or the theater scene from the original "King Kong," or maybe a nightclub act that wouldn't ave looked out of place in "Cabaret."

Why, no on even expressed any thoughts about the bodybuilder and his worship of the human form as an easily apt symbol for a narcissist-agnostic age. Asked during a workout at the Mid City Gym on Saturday whether a person could perhaps be too fond of himself, Schwarzenegger thought for a moment and answered, "No, I don't think so." Then he picked up a huge barbell and began a huff-and-puff routine.

He was followed about on this excursion by George Butler, who coproduced and codirected the film and coauthored the book. Butler said bodybuilding is just going to sweep the country and just everybody is going to get into it. He said Washington's own Alice Roosevelt Longworh was a big fan of Arnold's and could be expected to attend the Washington Premiere of the film next month.

This was news to Mrs. Longwroth, who said yesterday she has "no desire" to "see bodybuilders making muscles," She was questioned about her interest in bodies. "poeple's bodies?" she asked. "Or automobile bodies? Oh, I suppose if I had my way I'd have a collection of weighlifters running around and carry on a sort of barren castle on Dupont Circle."

Mrs. Longworth's granddaughter, on the other extension of the phone, scolded her for such talk. Mrs. Long worth laughed. "I'm not in the least interested in human bodies," she said.

Back at the gym, Arnold was asked if maybe just one day he wouldn't like to wake up as a normal sized person - like the rest of us. "Well maybe," he said, between glances into a mirror. "Sometimes I think it would be nice to walk down the beach and have people come over to talk to you about something other than your body, and maybe just for one day not have mothers dragging their little boys over and saying, 'Charlie, come over here, he's not going to hurt you,' and wanting to feel your muscles and asking me to tell their children they must drink milk. It would be nice maybe not to have that.

"But only for one day."