NEW YORK. Sept. 11 (INS) - The American Broadcasting Co. announced today that plans for a new network radio show featuring off-beat disc jockey Jean Shepherd, former Cincinnati radio figure, had been canceled. A spoke man said negotiations "fell through." but did not elaborate. The network last week said that Shepherd, who now is heard in New York on WOR, would start a nightly show for ABC about October 22. Shepherd said: "I honestly don't know anything about it, but my understanding is that there was a fight about the time my show was to go on."