“3rd Rock from the Sun”: NBC’s underwatched, giddy cartoon of a show comes up with a sweeps stunt that works. John Cleese guest stars on two successive episodes of the aliens-on-Earth series, making a brief appearance in a special one Tuesday (8:30 p.m., WMAQ-Ch. 5) before he is featured in the regular time period Wednesday (8 p.m.). Cleese plays a visiting professor not unlike John Lithgow’s Dick in temperament and self-absorption, but better at the earthly talents. He becomes a romantic rival for the attention of Jane Curtin’s Mary, and the dual hamming of Lithgow and Cleese, two masters of the trade, is a treat. Elsewhere, “Frontline” on Tuesday (9 p.m., WTTW-Ch. 11) looks at the American battle against marijuana, from its interesting history to some of the mom-and-pop growers to questions about whether penalties meted out to dealers are fair.
