"Sue!" a red-eyed Roy Cohn barks into the phone at National Airport. It could be a name, or perhaps an order. "I'm in a phone booth in Washington. Sue? Sue? Wait, wait, wait. Can you hear me? Tell them that Mr. Murdoch is calling tomorrow, by which time -- "

"Hi, it's Cornelia," Cornelia Guest is saying in the next booth over, where she slouches against the partition in a full-length fur. "How are you? Listen, I'm still in Washington."

But not for long. Cohn, the ubiquitous New York lawyer, Guest, the ertswhile debutante, and her mother, gardening columnist C.Z. Guest, left town around noon yesterday with a cartful of luggage, two Cavalier King Charles spaniels and an Afghan named Morgan on Cohn's red-white-and-blue, star-spangled Merlin 4 Turbojet.

Having missed the morning flurry of flights, they were somewhere in the muddle of the postinaugural exodus -- that inevitable rush of ennui after the music dies. Some celebrants left the good times behind yesterday in buses, trains and cars. Others -- like Frank Sinatra, seen skipping town Monday -- bowed out early.

Among the jet set waiting to board their gleaming Sabre 60s, Lear Jet 35s and other winged conveyances, the afterglow of Ronald Reagan's second inaugural blowout seemed to inspire less wistfulness than the first -- mainly because there were fewer jet-setters to be wistful about it.

"We have much less traffic than we had four years ago," said Patrick Dunlap, operations manager of Butler Aviation, National Airport's terminal for private aircraft. "I think there are a couple of reasons. First, the Super Bowl. And also the fact that this was Ronnie II instead of Ronnie I, so maybe people were less enthusiastic." Dunlap said he was expecting to handle about 80 takeoffs yesterday, about half again as busy as a normal weekday. That figure was seconded by Robert Reardon of Page Avjet Corp., which services private planes out of Dulles Airport. "It's the weather," suggested Keith Masten, Butler's adminstrative manager. "Plus there were only 6,000 people invited to this year's presidential gala, compared to 18,000 the last time. So I think there must have been 12,000 people with hard feelings, basically."

Waiting forlornly among the ashtrays at Butler Aviation, their bodies swathed in all manner of mammal, they looked like Russian gentry fleeing St. Petersburg after the fall of Nicholas II. There was Joe Morgan, a beefy Teamsters Union vice president, sinking into a padded chair. He was waiting for the union's Falcon 20 to bear him home to Fort Lauderdale and worrying what the weekend's frost in Florida had done to the grapefruit in his backyard.

"I don't want to cool out," Morgan said of the spate of partying. "I just want to warm up."

There was Kimberly Thompson, 22, the daughter of Jere Thompson, czar of Southland Corp. and the 7-Eleven empire, fretting over her Wednesday morning French class at the University of Texas in Austin. "I just want to sleep," she said.

And there were Cohn and his Guests, flashing sullen smiles.

"We've had the best time in our lives -- we've never stopped, we've never looked back, and now we're going," said C.Z. Guest. Morgan the Afghan, shifting her weight from paw to paw, looked vaguely unhinged.

"The dogs are great to have along to eat all the food," Cohn said as Cornelia puckered into the phone and hung up. "Everywhere we went, we ordered doggie bags."

"Oh, Roy," Cornelia Guest chimed in, "I left my boa constrictor at the hotel."

"It's to protect her from Charlie," Cohn said. Their mutual friend Charles Z. Wick, director of the U.S. Information Agency, was spied patting her posterior at an inaugural soiree.

"Oh Roy," Cornelia interrupted again, "who was it you told me to say goodbye to?"

But there was no more time for goodbyes. The Merlin 4 had taxied up the tarmac, revved up and ready for a flight to Teterboro, N.J.