The Academy of Motion Picture Arts & Sciences, which presents a little marathon called the Oscars, is calling upon all nominees to keep it brief. Their acceptance speeches, that is. "I've tried everything: charm, humor, persuasion, bribery," the March 25th ceremony's producer, Gil Cates, told Variety after Monday's luncheon for the nominees. Not only did Cates spread the word personally, but he offered some show and tell: film clips of past acceptance speeches. Alfred Hitchcock only said two words to the crowd when he got his gold. "Thank you." And off he went. Last year's program topped the record clocks, coming in at a yawn-inducing four hours plus. "You need to keep your acceptance speeches limited to 45 seconds," Cates told the assembled. "If, within that time, you deliver a moving, articulate monologue about what this moment means to you, all the better . . . Of course, if you've exceeded your 45 seconds, all bets are off." For safety's and ego's sakes, Cates promised that lengthier speeches could be posted in their entirety on the Oscar Web site.