CBS starts a science magazine with Walter Cronkite as host and you think we're going to complain? No way! It would take someone who hates Miss Piggy and loves the Ayatollah Khomeini to discourage a venture as rampagingly worthwhile as "Universe," which begins a trial run tonight at 8 on Channel 9.

Uncle Walter turns Mr. Wizard for this half hour of science-oriented features, test-piloted as a single broadcast one year ago. On tonight's opener, Cronkite introduces viewers to an autistic British child with an astonishing gift for drawing, some smart-aleck computers that cook up and deliver the ideally inoffensve political speech, the story behind those EPA mileage estimates in auto ads, and a doctor who is trying to find the psychological and physiological functions of crying.

Nadia's story is probably the most fascinating, and it opens the program. When she was 3 years old, the child, who had already exhibited most of the traits of autism, began to draw -- not just the usual spiked suns and stick trees kids usually draw, but pictures full of vigor, imagination and perspective. An art critic calls them the work of a "genius," but three years later, doctors whose treatments were designed to bring her out from the mysterious shelter of autism had also, apparently and inadvertently, cured her of the ability to draw.

Cronkite himself went to England to report the story, and fascinating as it is, it's incomplete as told here. The producers should have added an expert on the chemical components of the human brain, someone who might have offered some hypothesis to shed light on the mystery not only of Nadia, but of artistic expression itself, and the relationship betwen genius and what used to be called "madness."

Other stories suffer from insufficient evidence and the producers' nervousness that we might be becoming restless, the most common neurosis in all of television. The report on whether mileage tests are accurate is momentarily brightened by a General Motors vice president who with unexpected bluntness contends, "We aren't screwing the public on this, we really aren't."

And reporter Charles Osgood is good on a lab experiment looking into the nature of tears, although the scientist uses a primitive methodology: he peels onions at, and shows sad movies to, his control group, in order to produce those salty little pellets. Osgood says humans are "the only creatures on earth who weep" -- or need to, Mark Twain might have added.

One crucial problem with this excellent, wonderful program is the script by Dale Minor, which rarely will let pictures speak for themselves. Surely one goal of the program ought to be to invoke a sense of wonder about the world, but at the moment, it's too talky for that, and only the time-lapse "bumpers" used to separate the show from its commercials are sufficiently visual.

"Universe" may ironically be one of the few shows in television that needs more glitz and techno-chic. Cronkite's studio-bound intros and outros seem oddly old-fashioned and overly lecturely, but Cronkite's performance is not to be faulted. Not by anyone who doesn't want to be ridden out of town on a rail, anyway. Second City

"Live From the Second City," which is naturally on tape, brings some of the current comedy at Chicago's famous, star-launching cabaret to television Sunday night at 11 on Channel 5 for 90 uneven but fitfully sparkling minutes. s

Bill Murray of "Saturday Night Live" hosts the program and melts diligently into the ensemble of players for sketches that are only moderately topical but often quite, quite dirty. The program begins raucously with a sketch about a nun-run health clinic at which a humiliated Murray must seek treatment for a venereal disease and reaches its high point just past midway, with a pretty riotous burlesque of a suburban PTA meeting at which sex education is the inflammatory topic of the day.

The range of humor may not be very broad, but it takes in social satire ("I think I know a little bit more about your problems than you do," huffs an urban affairs major to a roomful of innter-city souls), shameless puns ("The Dumbrowski Dental. School for Students of Polish Extraction") and musical parody, including a visit to the Grand Old Opry. There it is observed in song that there's "too much sex and violence on TV, and not enough at home."

It sounds better than it plays, though, because the young performers, agreeable in varying degrees, play to the live audience in the club and haven't adapted their style to the TV camera, so that almost everyone but the seasoned Murray simply runs around screaming. The fever pitch quickly gets wearying, and only the terribly tolerant will make it through the whole show. Those who do are guaranteed some hearty if occasionally nasty laughs, and they will also see in the closing credits the names of executive producers Bernard Sahlins, original owner of the Second City club, and Paul Klein, once NBC's top programmer and now just another name on Freddie Silverman's enemies list. Time lurches on.