Among the events that turn up on the New York entertainment scene are readings staged in the hope of raising enough backer money to bring a project to fruition, as well as to try a work out on friends and those in the know. Accordingly, I hastened to the Public Theater on November 4th for a reading of Robert Downey's latest screenplay version of his "Rockaway Bob." I've long been a fan of Downey, the father of actor Robert Downey, Jr., dating to such very entertaining films as "Putney Swope," "Pound," and "Greaser's Palace." Downey is a man who thinks funny, whether on a page or in conversation.His latest screenplay is very, very funny indeed, with some sharp dialogue and hilarious situations. It was made even funnier, thanks to the performances of Steve Buscemi as a hard-boiled detective and Ann Magnuson as a ditsy dame who comes on to him. There was also a large cast on stage to round out the parts. The format was everyone in a row of chairs, but there were moments when Magnuson got up and danced and gyrated sexily. She was a show stopper. Others in the reading cast included Tony Arkin, Chuck Barris, Amelia Campbell, Randy Cherkas, Sue Costello, Hannnah Dalton, Brian Donowho, Jim Downey, Burtt Harris, Marcia Jean Kurtz, Larry Loonin and Alice Playton. One could easily visualize the work as it might appear on screen. Take note.