CBS News has peeked down from its imaginary Olympus and learned a thing or two from the independent filmmakers who've done documentatries for public TV. "CBS Reports: But What About the Children?" at 10 tonight on Channel 9, uses impressionistic and cinema verite techniques already perfected by such industrious pioneers as Frederick Wiseman, Alan King, Alan and Susan Raymond and L.A.'s TVTV.

Producer-director Grace Diekhaus decided to build her report on American divorce around a single family, not a parade of examples and statistics, and study the effects of rhe splitup on one pair of children. Despite some questionable priorities in the editing of the finished film, the one-hour documentary makes a number of social abstracts immediate and strikingly graphic.

Just how representative Leon an dCarol Goodman of Phoenix, Ariz., are we don't really know, but their two sons, 9-year-old Greg and 6-year-old Todd, are models of understanding and endurance. Often the camera finds them lookin sad, confused or lost, but by the time the program is over, their stamina and powers of adjustment are very impressive.

They're also media-bright in the way more andmore children are getting to be. They eve take over the interview chores for producer Diekhaus. "Hey Todd, how do you feel about Dad?" And: "Hey Todd, how would you feel if we lived with Dad instead of Mommy?"*tThe parents are much less sympathetic. Leon says he thinks "women's lib" caused the divorce. Carol spouts the I-me-mine dogma of the self-obsessed '70s: I like who I am now more than I've ever liked who I am." Big deal.

While Mommy Dad exchange trendy cliches and volley for serve in the sex-role sweepstakes, the kids fend for themselves or are looked ofter by Keith, a 21-year-old employed by Mrs. Goodman so she can go off to political fund-raisers. The family rituals that look so rousing and resonant in "Who Are the DeBolts?" seem cold and mechnical here, and when Todd finally breaks into childish tears near the family pool it is all too easy to empathize with him.

Unlike the network's popular "60 Minutes," His "CBS Reports" does not constantly coax and force-feed a point of view. It leaves viewers free to draw conclusions of their own, but few of these options offer much in the way or encouragement about the American family unit.Diekhaus is to be congratulated for letting the kids speak for themselves and for not yielding to the TV urge tooversimplify.