Alfred Kahn, who doesn't know one airplane from the next, who once said he felt like telling Pam Am to go to hell, then later said he didn't have in mind a new route, is boarding a Northwest Orient 727 at National Airport. At the plane's door, propped upright, is a guitar case. "Mmmmm," Kahn says, "I think if it's under 12 it should at least get half fare."

He could almost make it as a stand-up comic Henny Youngman of the bureaucracy belt, this thin, small, 61-year-old man with the balding head and comic-opera face.

Strapped in his seat in coach, one leg propped on a hugh orange briefcase, he suddenly confides - almost whispers - to a scribbling reporter: "It's very important to realize you're not God."

Not that it's all just yuks and good times with Jimmy Carter's chief inflation fighter. There is a warty, lizard toughness to Alfred Kahn, too, something that helps explain his startling 16-month success as chairman of the Civil Aeronautics Board, when America's airlines cut their fares like confetti - and began to realize the biggest profits in history. That was Alfred Kahn's doing.

Alfred Kahn, who came to Washington a year and a half ago not exactly kicking and screaming, who still takes the subway to work (and swims in the neighborhood pool), who still sometimes pads around the office in his socks, is the kind of antibureaucrat who can say:

"Look. I wake up every morning and tell myself this whole thing's a joke. You know: cover of Newsweek with the president, guest shots on 'Meet the Press.' It's a play, a performance. I'm always prepared that it's Sunday night and the curtain's coming down. A year from now people will say, 'Who's he?' . . . and that'll be all right.

Alfred Kahn says this staccato, like most everything else. Only there's no punch line.

He looks a little like a small, furious bookkeeper.At the moment, at 30,000 feet, somewhere between Detroit and Milwaukee, the escaped economics professor from Cornell is buried in a spiral notebook drafting a speech. The notebook is full of arrows and exclamation points and all manner of marginalia - jokes, dates, percentage points. There are scribblings in black ballpoint and scribblings in blue ballpoint. The black ones are from last week's talk - in Hartford, the blue from the week before - in St. Louis. "Just to show you I'm always evolving," he says. Today's show is both black and blue.

The one-time college dean glances up, peering from behind thick tortoise shell glasses. He can't recall a statistic. He pounds a fist in mock fury.

"It must have been that drink I had last night."

"But, Fred, you didn't have a drink last night," says Mary Kahn, a kind, quiet, grandmotherly woman who still looks confused by her husband of 35 years.

"Oh. It must have been that drink I thought I had last night."

The man across the aisle wants to shake. (He has just recognized who this is.) "Oh, I'm delighted," says Kahn. "I'll have to be careful what I say now. Hey, got any ideas on inflation?"

When Alfred Kahn took over the CAB, he wrote a series of memos to his staff on the subject of Washington gobbledygook. He demanded people around him use plain English. He recounts this, wreathed in a villain's grin. "I told our lawyers, 'Look, why don't you go home and try talking like that to your children, and if they don't laugh you out of the room . . . well, who wants children like that?'"

Hold the laugh track; ham on wry:

"When people in Birmingham die, they don't know where they're going. Only that they're changing planes in Atlanta."

Says Elizabeth Bailey, board member of the CAB, a presidential appointee who worked closely with Kahn: "He'll steal a joke from anybody. Once I had lunch with him and another man and the other guy got off this terrific line. Before the lunch was over, Kahn had this little book out writing it down. He's not proud."

Bailey says she's a little worried about Kahn in his new job: "He's all alone over there. He needs a staff. That's when he works best."

Says Mike Roach, Kahn's personal staff aide at the CAB who has now quit Washington for San Francisco: "The guy's always on. Of course he's more on when there's an audience." Roach, like Bailey, is an ardent Kahn supporter. Morale was sky-high under him, Roach says, even though in effect people were working to eliminate their jobs.

By his own admission, Alfred Kahn is a workaholic. People around him find they generally keep the same pace. Or quit. He swims and jogs and skis. He can talk you down. He will quote Robert Burns and sing Gilbert and Sullivan. He says he would trade his whole career for the role of the lawyer in "A Little Night Music." It's nothing for him to read The New York Times, watching the evening news, and dictate chapters of his latest book - all at once. "My record is four things at once," he says.

But the economy has taken center stage.Is there a danger in the country getting "monomaniacal" about inflation. "I already said that in an interview," he says, before the question is fully out. "Don't quote me to me."

Alfred Kahn stops everything to help his wife on with her sweater. "Actually," he says, "I'm the ham in this family. Mary and the children are the artists." Recently, he took Mary to Venice for a kind of second honeymoon.

Alfred Kahn, whose 28-year-old daughter Hannah is a professional dancer and lives in New York with a musician ("We call him the spouse equivalent") has been hamming his way from one career success to another for over three decades now - ever since he left Yale with a Ph.D. in economics. (He had earlier graduated - at 18 - summa cum laude from New York University.) That career has consisted of stints in the army and the antitrust division of the Justice Department, of writing landmark books on the economics of regulation, of serving on boards with such names as the National Academy of Sciences Advisory Review Committee on Sulfur Dioxide Emissions.

Mostly, though, it has consisted of college teaching. Alfred Kahn put in 27 years at Cornell, where he still has tenure and a fine old house near Lake Cayuga, and where he was alternately chairman of the economics department, a member of the board of trustees, and dean of arts and sciences. "A dean is to a faculty as a hydrant is to a dog," says Alfred Kahn, his pan dead as dishwater.

In his new job, the wit will not be unwelcome. What with grouchy consumers and a worried president ("Will you help me?" he pleaded to the nation), what with inflationary spirals turned into political footballs, what with an emaciated dollar and a cantankerous Teamsters Union (for one) which might not feel like honoring the president's 7-percent solution comes contract expiration time next spring. Already, there seems a baiting effort on the part of some of the press between Kahn and crusty AFL-CIO boss George Meany.So far, Kahn has only nibbled.

A week ago Alfred Kahn made headlines by saying the country could be in store for a "deep, deep depression." The next morning, the President of the United States labeled that "idle talk."

Alfred Kahn made $52,500 at the CAB. As chairman of the Council on Wage and Price Stability and Advisor to the President, he makes $57,500. That is a 9 1/2-percent increase.

"The only thing I have is my independence," says Kahn. "I will not weigh every word." He will not be a jawboner - or arm-twister. "If he wanted that, he picked the wrong man."

Once, when Jimmy Carter overruled him on an airline decision, Kahn snapped that that was the president's prerogative - and his was to disagree.

Kahn sprung himself from academics in 1974, when he went on leave from Cornell to become chairman of the New York State Public Service Commission - and proceeded to wreak havoc. He began making the telephone company charge callers for directory assistance, on the principle of "marginal cost pricing," so he could give most of them credits back every month.

Following Kahn across the country, watching him foxtrot with the press, gladhand strangers who have seen him on the tube or in People magazine, one can't help be struck by how the old teach is having the time of his life. "I'm 61 years old," he tells the audience in Madison, dipping his shoulders, turning up his palms. "What am I saving it for?"

In fact, what Kahn sometimes wonders late at night now is whether he could ever go back to that sherry-and-camembert cocoon he came from (though he thinks cocoon is the wrong word). He's had a gulp of fame, warmed his hands at the media fire. Going back to a world of theory might seem like Florida retirement.

"It was a potential I always secretly thought I had, doing this," he says. "It's a new flowering. "It's exhilarating." Yes, he knows he's been "picked up" by the president for this fight. That's okay: He deserved to be picked up, he thinks. He was the best free agent for the job. There was a demonstrable success behind him. Washington loves demonstrable successes.

What this fight is really about, says Kahn, is "turning the American spirit around." The hands are up in the air - a teacher making a point. "It's absurd to think anyone can do that." Pause. "I'll try."

Alfred Kahn is not unaware of the mine fields of the Washington Ego. He knows he isn't the only strategist in the inflation war. There are also a secretary of the treasury and a chairman of the council of economic advisers and a special trade representative, to name just three. There is a thicket to go through.

"My wise Washington friends all tell me it's going to be trouble, that all these other boys - Blumenthal, Schultze, Strauss - will want into the game. There are bound to be bruised egos. 'You don't know how tough the Washington game is,' they tell me."

A sudden, flinty look. "I do not have to demonstrate I'm more powerful than Ray Marshall or Juanita Kreps. My ego doesn't depend on it."

What about the public expectation of him after all this press? "Well . . . screw the public. I know who I am."

What has seemed most appealing about Alfred Kahn, besides his wit, is his ability to snap through the bureaucratic jabberwockey. (His memo on gobblegook concluded with, "A final example of pomposity, probably, is this memo itself.") Some would say his style borders on intellectual arrogance. It may be the confidence of the successful outsider, someone who has a net beneath him.

"The airline executives knew they couldn't touch me. That can be bad, of course. I didn't want them to think I was just in it for the intellectual challenge. Which I was." A slow ooze of smile.

He has relished the flip remark. Told once his plan to cut air fares to Europe would seriously jeopardize the North Atlantic fare structure, he supposedly shrugged and said, "That's a good afternoon's work." He has said in hearings he wanted "to get government's sticky hands off airplanes." He has talked of the "straight-jacket of bureaucratic controls."

"I began with the ideological conviction that airlines could stand to be as competitive as possible. Open up the doors: That was the principle. But with inflation, there is no easy principle. Licking this one involves exhortation, moral suasion, walking a balance of fiscal restraint on every side. "It's the peculiarity of inflation that it feeds on itself. "It's the nebulae, the amorphousness of it, that will defeat you."

He has finished his airline snack and his speech now. He has changed planes in Milwaukee (where Northwest left his bags.) And he has bumped into an old student. David Kairys is a Philadelphia lawyer. He had Kahn in a seminar at Cornell. Kahn signed a card for him that cut through red tape and allowed him to stay enrolled another year. He sees Kahn now and thanks him all over again. Kahn looks almost touched. "It happens all the time," says Mrs. Kahn. "He meets them everywhere."

"How is your speech, dear?" she asks.

"Oh, it's terribly funny. Of course I think everything I write is funny."

They talk of family. There are three Kahn children, all grown. One son is an anthropologist living in London. A daughter is married to a Louisiana State University poet. "I accept all speacking invitations in Baton Rouge," says Kahn, "on behalf of my grandson." (Mrs. pulls out a picture here.) Also in the Kahn family is a nephew just back from the Peace Corps. The Kahns raised him since he was 12.

The stewardess comes by for his plastic tray of plastic food. Kahn: "It's inevitable that a great upsurge in traffic will be accompanied by a decline of certain quality. But this . . . is ridiculous."

Kahn and his wife met in Washington during the war, Mrs. Kahn says. She was working in housing, he with Justice. Eventually he moved to Commerce, then to the War Production Board. Which he hated. "I wrote to my draft board and said, "What happened?" I had a deferment for my Ph.D. A month later they told me what happened. I was drafted."

But not before Mary Kahn and her roommate went to a madrigal singing group one night. Fred Kahn who grew up a "Pandlot singer," was there and walked her home. Sixteen months later they were married. He is still singing to her - and to anybody else who'll listen. He has played the Lord Chancellor in "Iolante." He's memorized a lot of the "Mikado," in which there's a tune with a line: "He's got 'em on the list - he's got 'em on the list; and they'll none of 'em be missed."

Kahn has a lot of people on his list these days. He has already indicated he would like to deregulate trucking. He reportedly had a firm hand in last week's textile and beef presidential vetoes. Don't expect miracles in his constant message. "Small victories."

He came into economics in the Depression, he says, when the world looked awful. "Economics is the gloomy science. Theres always a certain pessimism in that everything has a cost." Honest economists, he says, are always anti-politicans.

One regret: That his father is not here to share in all of his success. He was an immigrant silk mill worker from Russia. His son was born in Paterson. N.J. "He never had this world knocked."

"You know, Mary and I were in Venice for a week last month. It was our 35th wedding anniversary. I had my mind on work. But it was nice to relax, too."

Hovering here. Feeling maybe just a little sentimental. Some sure inner clock says change the tone. "You know, I want to memorize all this for my grandchild. And he'll say, 'But, Grandpa, what did you do after November 1978?' and I'll say, 'Shut up, kid, we don't go into that. . . .'"