Re ''You Won't Hear a Refrain of 'All That Jazz''' [Sept. 7]: The notion that serious mainstream jazz cannot sustain an audience on Long Island ignores the fact that there are several clubs and individuals that are working to perpetuate the art form. Al Cardillo, for example, has continued to present major world-renowned musicians three times a week in various locations throughout Long Island consistently for the past seven years. His efforts not only have single-handedly provided an outlet for New York musicians to jam informally but also have provided the general public with a taste of the best in mainstream jazz.