Take one part ''Lou Grant'' and two parts ''The Mary Tyler Moore Show'' and there you have a new show - ''Jessica Novak'' (CBS, Thursdays, 10-11 p.m.). Partly correct. What you have is a fine try at clone-programming, which comes off better than most but not nearly as good as either of the originals. ''Jessica,'' a TV reporter played by Helen Shaver, just doesn't have that mysterious MTM ingredient, although David Spielberg as Jessica's Lou Grant-type boss, Max Kenyon, does have the empathetic Ed Asner ingredient.
All in all, ''Jessica Novak,'' produced under the aegis of the dependably tasteful executive producer Marc Merson, is off to a good start. And just as both Mary and Lou faltered a bit for a few weeks before they really took off, it is possible that Jessica and Max may do the same.