His fantasy is to be Zero Mostel. He hates stuffy memos, stuffy people. In the midst of an interminable meeting of bureaucrats he's likely to begin cutting up, "consciously hamming it up," as he puts it, "to induce a kind of freedom."

For economist Alfred Kahn-appointed by Jimmy Carter to head his anti-inflation program-Washington is a city ripe for the pricking, and Kahn's obvious love for blunt talk has worried some White House insiders.

When Kahn was chairman of the Civil Aeronautics Board, he rode herd on a staff of about 900, delighting reporters with his wisecracks, pleasing some airline execs with his brisk introduction of free enterprise to an industry hamstrung by government rules.

Kahn was a character, everyone agreed, and the federal government needed more like him. But when Carter brought Kahn to the White House last October, his quotable quotes kept coming. He referred to Arab oil producers as "shnooks," and, at another time, opened a press conference by telling a Jewish joke that brought down the house. He is-with his Steve Allen glasses and rapid-fire, straight-faced delivery of one-liners-a funny man whose tendency to answer questions boldly reportedly led White House image master Gerald Rafshoon to remark to a colleague: "I'm going to have to help Kahn out."

Behind that comedian's demeanor, however, is a 61-year-old Cornell professor with a long interest in the issue that underlies his new job: What is the government's role in regulating private industry?

In the early '70s, Kahn wrote The Economics of Regulation , a study that led to a request by Nelson Rockefeller that Kahn head New York's Public Service Commission. There, Kahn oversaw such things as electrical rates (he introduced a pricing system that gave breaks to users during non-peak hours) and telephone service (he permitted Bell System competitors to hook up to the the giant's equipment).

In the spring of 1977 it took a private chat with Carter and a persuasive call from Edward Kennedy to convince Kahn to reverse his initial decision to decline the CAB chief's chair.

"I'm not immune to flattery, having been a professor all my life," Kahn explained coyly later. He prospered at the CAB, eliminating regulations and pushing airlines to compete as he struggled to "unconstipate the bureaucracy." Kahn said he found he was a fair politician, thanks partly to four years he spent as dean of arts and sciences at Cornell.

"You may have heard a dean is to a faculty as a hydrant is to a dog," he said to explain his political alacrity.

Kahn will need all the silver-tongued prowess he can summon this year as he begins making a series of appearances on behalf of Carter's get-tough wage and price guidelines. Shortly after he moved down Connecticut Avenue from the CAB to the White House, Kahn said if America didn't heed presidential advice, a "deep, deep depression" could result. At that, the stock market tumbled, and bureaucrats experts at speaking around any subject shuddered that anyone would sacrifice obfuscation for such stark specificity.

So Kahn began substituting the word "banana" whenever he meant "depression." Suddenly a sense of humor began to infiltrate discussions of the normally dry world of GNP, balance of payments and cost of living indexes.Now Kahn, who sometimes calls himself "the powermad professor," finds himself in an unusual situation: for once in Washington, the bearer of bad news-the man who warns of dire consequences if thrift and self-sacrifice don't become words for Americans to live by-is a welcome messenger.

If Kahn's jawboning and his boss's programs fail, Americans may at least march into a deep, deep banana laughing all the way. CAPTION: Picture, no caption