Throughout his academic career, economist Alfred E. Kahn showed a penchant for comic opera - seeking the comic lead in the annual Gilbert and Sullivan production at Cornell University.

But there is nothing funny about Kahn's new role as President Carter's new counselor on inflation.

After agonizing over the decision for nearly a week, the former Cornelldean, 61, reluctantly agreed to take the difficult new job and give up the chairmanship of the Civil Aeronautics Board, where he won President Carter's admiration for stimulating competition in the airline industry.

A year and a half ago, a reluctant Kahn was induced to leave a three-year stint as chairman of New York States Public Service Commission where Carter told him, "I need you."

"I don't often find myself in a position of turning down a president," Kahn said afterward.

Kahn comes to the new post with excellent credentials.Besides a distinguished academic career at Cornell, he served as a staff economist at the Brookings Institution and on the senior staff of the Council of Economic Advisers in the mid-1950s. He is the author of four books and scores of articles.

Before accepting the job, however, Kahn set down a few conditions. "It's got to be compatible with what I've made my reputation on and what I believe I'm good at," Kahn said in an interview Monday afternoon while he was still negotiating with the White House. "I'm not a price and wage fixer.

"That doesn't mean that I feel it violates my sense of intellectual integrity to see what you can do to affect strategic wage and price bargains, but it isn't my forte," he said. "I'm not an arm twister. I'm not a jawboner.

"So if the job is defined principally as being the administrator of a wage-price guidelines program, it's really not for me."

"If, instead, it is defined as the president's adviser on inflation, so that it enables me to play an important role in the whole range of government programs that inflate costs, that obviously is congenial to me."

Kahn said he believes it is more important to find a longer-range solution to the problem of inflation than to concentrate on particular wage or price increases. And he said he doesn't think mandatory controls are the way to do that, "except on an interim basis."

It was a conversation initiated by the president Monday that persuaded Kahn to take the inflation post. "His conception of the job is amazingly like the one that would be congenial to me," Kahn said.

"The conversation was so open . . . that I think even my University of Chicago friends who don't believe in any wage and price controls would have difficulty in thurning this one down . . . ," he said.

Before accepting he said he required assurances that members fo the Cabinet and others in the White House understood he was to have direct access to the president and that it was "clear that it's not to appear to the public to be primarily a wage and price administrator."

He is not sanguine about the prospects, nor is the public. "The chances for success - demonstrable success - are far less than what I had" at the CAB. "I think you're dealing with something that's 100 times more important, but your chances of success are about one-thousandth."

Although the new assignment is "dangerous" to him personally - "I don't like to fail," Kahn says - he said he had o ask himself. "What am I saying if for - my reputation?"

His reputation is exemplary. He came to Washington with a reputation as an innovator already established. Under his leadership at the New York PSC, for instance, New York was the first state to permit telephone users to book up their own equipment to the Bell System. He also introduced time-of-day pricing for electrical rates, offering lower prices for electricity used during period of lower demand.

In Washington, he has come to be known for keen intellect, analytical mind, quick wit, candor and clear speaking - a trait he has demanded of the CAB staff in all letters and documents. Please try to write board orders, an especially letters for his signature "as though you are talking to or communicating with real people," he exhorted attorneys in a widely publicized memorandum sent around the CAB in his first week in office.

At the CAB, Kahn pushed the board to strealine cumbersome regulatory procedures and inject competition into the airline industry, efforts that have already produced lower fares, increased air service, more passengers and higher industry profits."I just open my mouth and a fare goes down," Kahn once quipped.

But Kahn says he doesn't believe the market system is perfect and that he favors government intervention where the system had failed.

Nor is he a prisoner of his past views. The architect of the present two-price system for regulating natural gas, he now favors an end to regulation.

In the months ahead, his openness to change is like ly to be put to an even greater test.