"You had the coat," Robert Wagner deadpans, as the guy helps him on with a double-breasted camel-hair topcoat. So droll is this Wagner of the big shoulders, eyelids heavy with tan, a lizard spun out of purest cashmere.

"I had the coat all the time," says Dulles Airport, where they're shooting "Airport '79 Concorde," is telling other people where to carry things: aluminum suitcases, stepladders, cables, walkie-talkies, lights, reflectors, all of it scattered across the waiting room, a technological sea lapping at the feet of a dozen autograph hunters.

"Oh, you had the coat," Wagner says, as the guy helps him on with it. Wanger doesn't have to shrug, squirm, shoot his cuffs. The coat just fits.

"Yeah, I had the coat," the guy says, at ease with all this absurdity.

"You had the coat," Wagner says. The merest vapor of a smile drifts across his lips, subtlety verging on decadence.

He rambles off towards the windows where the director, David Lowell Rich, is setting up a shot in which Susan Blakely, playing a TV anchorperson, rolls off in a mobile lounge to a waiting Concorde for a flight to Paris.

Evil millionaire industrialist Kevin Harrison, played by Wagner, sees through the window that she's reading the crucial documents as she goes, documents which prove that he's a bad guy; and now he'll have to try to blow the Concorde out of the air with missiles.

"She has looked at the documents," Rich announces, to no one, or perhaps everyone, in particular. "She realizes the implications. She sees Harrison watching her. She knows that he knows."

The movie is the great-grandson of the original "Airport," with scions being "Airport 1975" and Airport '77" plus a variety of declasse made-for-TV cousins in the airplane disaster genre. Except that the director disputes this thesis utterly and finally.

"The story line fulfills all the Aristotelian requirements for drama," says Rich, who is a beak-nosed man in a brown sweater. "There is no question in my mind that this is not just another 'Airport.' It could be any drama, but it happens to be about an airplane. It becomes a kind of 'Grand Hotel.' The catalyst is a classic kind of usage of people. It's a 'Bridge of san Luis Rey' . . ."

Well, roll'em. The mobile lounge pulls away from the terminal. Wagner watches with astute grimness. Inside it, BLakely looks at the documents, appalled. Cut. Okay, everybody.

Wanger is through for the day, though Blakely has more shooting to do. He wanders back to the terminal looking not as if he owns the airport, but as if he used to.

"I just finished shooting a pilot film called 'Hart to Hart,' last week," Wagner says. "Then I flew over to Paris to do the shooting on this, then flew back in here on the Concorde. Wonderful plane."

The autograph types close in. Wagner has the technique of establishing absolutely no rapport with them at all, though he provides an elaborate signature that looks like a cardiograph readout which is very bad news indeed.

He is asked if he has star billing in the picture. The questioner means top billing, but there's a big distinction. The vaporous smile rises again. The questioner, seeing his mistake, laughs. Wagner trumps him with a major back-of-the throat laugh which does not alter his droll blue-eyed stare.

"Think I'll go back to the hotel." Wagner says cheerfully then. "Call the Coast, get a few bets down . . ."

By now, the whole production mob, save Wagner, has stormed onto the mobile lounge extras, gaffers, grips with director Rich welcoming even more abroad for the last shot of the day, a close-up of Blakely looking at those documents.

"Is her right eyelash okay?" Rich inquires in a tone which says her right eyelash is definitely not okay. So Susan Blakely's make-up girl, Hallie Smith-Simmons, picks up a bag of brushes which could have outfitted a trompel'oeil painter of the 19th century, and the eyelash becomes okay.

"Okay, get talking, background," Rich yells to the loungeful of extras, who proceed to favoricate the sort of hipsprung grace and cheer which has never been seen in the surly lethargy of any real airport.

Three takes later, Blakely has made the awkful truth of those documents truly awkful enough, even cooling her sad forehead against the chrome pole she's been leaning against.

"Flats!" she cries, shucking preposterously high heels and slipping into low-heeled boots to run down to the Delta airlines VIP lounge for a glass of orange juice.

Blakely made a star-sized name for herself in television's "Rich Man, Poor Man," but since then, "the problem has been scripts. I signed to do a movie about a ski champion, but we can't get a good script till the snow has melted. I just finished 'Dreamer,' where I play a midwestern countergirl, we filmed it in Alton, ILL. or someplace, it's the best role in the movie, though not the biggest," and now she's talking so fast you can hardly understand her and besides it's more interesting to watch how she keeps glinting her blond hair around, and that smile! Ah, it's bow-shaped, with the middle of the upper lip just a hint lower than the sides, and the teeth beneath can't back in just a bit an (underbite?) to make her look shy and eager at the same time.

She'll need all she's got. As the director has already pointed out, the Concorde is the real star of the movie, and the producer later confirms that it will get billing above all the stars, who will include Alain Delon, Cicely Tyson and George Kennedy.

Playing against dogs or children is hard enough, but an airplane?

Blakely lets fly with a high, huge burst of laughter which she breaks, suddenly, in mid-peal, to say: "I like playing against dogs. I love playing against children. I love children. But we're not shooting that much on the plane, are we? I mean, we have a mock-up in California for all the inside scenes, though of course in Paris we shot . . ."

In another phrase or two, she's cranked the speed of this spiel past the understanding barrier, making up with her loquaciousness for Wagner's big-beef cool - having learned the same thing, perhaps, that they never listen, they just want to look. And get your autograph.