WESTWARD THEY COME. BIG BUCKS FOR BIG BOOKS BY PAUL ROSENFIELD Today's authors who deliver filmable materal are in the midst of their own inflationary spiral. This -part series deals with cur*ent hot properties -the books, the star writers, the bucks. Rosenfield interviewed more than 40 sources in New York, San Francisco Ind Los Angeles. Today's segment covers the novie deals and deal makers. EW YORK-At Elaine's, a famed N writers' Publishers watering Row, the hole, and indications all along are clear, that one trend is now overlapping another. The Big Book era -one true phenomenon of the '70s-has begun a shift. to California. Finding a major publisher in Manhattan last week wasn't simple: Simon & Schuster's -in-chief Michael Korda was returning from Los Angeles just as Delacorte boss Ross Claiborne was arriving. In September, Random House's David Obst will relocate in Hollywood. At a trendy Madison Avenue bookshop, one customer suggested subtitling the best -seller section "California." The fact is that Los Angeles -in terms of per capita sales -is now America's biggest book market, and Southern California now has the largest number of library checkouts in the world. Deal making, too, is emanating more and more from the West Coast. It's different than