YOU GOTTA HAVE WA, by Robert Whiting. (Vintage, $10.95.) An American journalist finds that in Japan baseball is taken with a seriousness that might astound even the most avid American fan. "Put down the heavy tomes on United States-Japan trade policies," Robert J. Collins said here last year. "Robert Whiting has hit upon a brilliant way of demonstrating the very different psyche of our major trading partner across the Pacific."