■ WORTH MENTIONING ■6:00 0 @ PREMIERE The 21st Century: ‘The Communications Explosion.” The revolutionary potential of communications is the premiere broadcast for this new color series featuring Walter Cronkite as reporter. In 2001, the broadcast indicates, man will communicate rather than commute. Expanded use of communications satellites will bring the most distant places into instant contact, and people will spend more time communicating with machines. Joseph Weizenbaum, computer scientist at Massachusetts Insitute of Technology, demonstrates an experiment in which he takes the role of the patient and a computer the role of the doctor. Other participants include Arthur C. Blake, British science fiction writer who wrote, in 1945, a technical paper in which he proposed a worldwide communications system via orbiting satellites; John Diebold, an authority on automation, and John R. Pierce, director of communications research for Bell Telephone Laboratory, Murray Hill, NJ.6:30 O 9 The Bell Telephone Hour: 'The Sounds and Sights of San Francisco. This one-hour color program shows the varied musical life and many of the impressive sights of San Francisco, with stops at the San Francisco Symphony conducted by Josef Krips; at a Stern Grove outdoor concert by jazz musician John Handy; at the San Francisco Ballet School where a class (with choreographer Lew Christensen) performs excerpts from Raymonda” ballet; a visit to the home of pianists Peggy and Milton Salkind; and the San Francisco Opera where director Kurt Herbert Adler conducts an outdoor performance.