You're only as good as your last movie's receipts, and no one knows it better than Robert Altman. The maverick director's 1994 Ready To Wear racked up a scant $11.3 million, so when he announced his follow-up, Kansas City, a '30s-era gangster flick, New Line and Miramax (distributors of The Player and Ready to Wear, respectively) reportedly said they'd wait and see. Now in post-production on the $20 million film (starring Harry Belafonte and Jennifer Jason Leigh), Altman is returning to the lion's den. ''It's being screened for three or four studios,'' says the film's publicist, Mike Kaplan, who insists, ''There haven't been any difficulties finding a distributor...it's a Robert Altman movie.'' Ah, but how much of Hollywood still sees Altman as a player?