All this fuss about the movie "Missing." (Its premise, recall, is that Americans approved a "kill order" for young journalist Charles Horman in Chile.) Meanwhile, Rather Rightish columnist John Lofton's been brooding about the author of the "Missing" book--"The Execution of Charles Horman: An American Sacrifice." Poking in his capacious files, he dug up an Ancient and Wondrous scrap: Author Thomas C. Hauser's "Martin Bear" connection. Remember Martin? A "nine-year-old San Franciscan"? He wrote letters to political biggies in '75. They were published in The New York Times, along with the replies. (Ear, which just poked in its capacious files, only shivered at one: "Dear Senator Buckley: In school today, we had to write someone we like and someone we don't like. You're the one I don't like. I think you're stupid. Your friend, Martin Bear." "Dear Martin: I am always interested in the opinions of my young constituents. Thank you for writing. Sincerely, James L. Buckley.") Martin was a star. He was made an honorary appointee to the New York City Youth Board. Then, oh dear. Martin turned out to be a three-inch-high stuffed teddy bear belonging to our Tom Hauser, who sort of wrote the letters for him. After Tom 'fessed up, The Times apologized lavishly to hoaxees: Sens. Kennedy, Buckley, Javits and Humphrey, as well as Mayor Abe Beame--to whom he'd sent 10 cents to save New York--and Bella Abzug, who had promised to frame Martin's rather odd drawing of her. And then we all forgot about him. Ear, short for bEar, is still writing this column itself. Stay tuned.