IT BEGAN AS A news story in the Santa Barbara News Press last month, but it was picked up by the wire services, so it traveled from the California coast to the rest of the nation. A seven-year-old boy named Edourard, who knew he was dying of leukemia, reassured his mother that he had been born before and would be born again, decribed in vivid detail his past incarnations, made plans for his own burial and, at the last, said: "Mother, turn off the oxygen. I don't need it anymore." It was a story to raise the hairs on the nape of the neck. Howard Kaminsky's nape prickled, and he called his west coast editor, Chris Conrad, to chase that story down and see if there was a book in it for Warner Book. Warner had already had a number-one best seller in a novel of reincarnation, Audrey Rose , and interest in life after death probably hasn't been so strong since the Etruscans. Well, there was, of course, a book in it, or I wouldn't be writing this. That original story of Edou's death, the one in the Santa Barbara News Press , was written by Bill Downey, a newspaperman and novelist. Bill and his wife Kim have a child in the same special school that Edou attended, and the boy was often in the Downeys' home. They were devoted to him, and Kim thought he was so remarkable that she tape-recorded him, his thoughts, his ideas, his mystical belief that he had lived before and would live again. There was not only a writer and tapes, there was an agent, perhaps the number-one literary agent on the west coast, George Diskant. Warner's Chris Conrad listened to the tapes in Diskant's office and heard the odd mixture of little boy and old soul. She advised Kaminsky to move fast. Which you have already guessed that he did. So Bill Downey is now writing Edou ; Warner has bought all books rights; there may be a hardcover book sale, and Diskant, of course, thinks it's a natural for movies or television. We cannot tell you what little Edou himself thinks of any of this, but if you hear ghostly laughter from another plane . . . light, childish laughter . . . don't write and tell us about it.