"I've moved into a job that doesn't exist with responsibilities that are invisible and with a staff that is yet to be assembled," Alfred E. Kahn, President Carter's chief inflation fighter, said yesterday.

Kahn's assessment of his monthplus job was made at a farewell party thrown him by the staff of the Civil Aeronautics Board to honor his 16-month stint with them.

"I feel as though I've left a family," Kahn told the hundreds of well-wishers during an emotional farewell laced with the humor and the free-speaking ways the CAB staff had gotten used to but the White House has just learned about.

In a reference to some White House staff unhappiness about his use of the word "decession" and later the substitute "banana," Kahn said it found it difficult to "act with contrition" when anybody remonstrates with him against using plain English. "I hope therefore that you will all interpret my famous reference to banas as a kind of mockery of the people who say, 'if you don't see it, it ain's there'."

On tables loaded with home-cooked goodies and a large cake depicting the White House, the CAB staff also had placed a large bunch of bananas with a red ribbon, which were given Kahn. "Look at all those wonderful yellow depressions," he quipped.

Asked later how he came to use the word "banana," he said "It just happened to come into my head -- and that's the secret to my problem." During his short speech, however, Kahn insisted that he does intend to be "discreet."

"I do recognize that I'm in a situation in which what I say apparently may have an effect on what I'm observing," he said.

More than once, Kahn replied that "Thank you, I need it" to those in the reception line who wished him luck. "Stiff upper lip," one CAB staff member counselled him.

New CAB Chairman Marvin S. Cohen told Kahn during a short presentation that he was finding it "impossible to fill your shoes" but was having fun trying. He noted that he was introduced at a speech last week by Art Buchwald who, noting that his predecessor had become inflation czar, "wondered what punishment the White House had in store for me."