Margo Kaufman is strong on male psychology in "The Silent Partner" (June 4), but she's weak on her movie history. Gary Cooper was hardly the strong, silent type. If Kaufman has ever seen "Mr. Deeds Goes to Town," "Meet John Doe," "The Real Glory" and "Love in the Afternoon," she will recall an actor who--with the help of some excellent screenwriters--had no trouble finding his tongue when it came to expressing his thoughts and feelings. Cooper's reputation as the "yep and nope" man comes from impressionists who, over the years, have turned him into a laconic macho man.