IF there's a lesson to be learned from the 30-year struggle between commercial broadcasters and children's TV activists, it is this: Nothing much happens to uplift what kids see on the tube unless outside pressure - from parents' groups, the government, or both - is applied.
The current rating system for American films, of some help to parents, resulted from parental/congressional leaning on the movie industry. Now it's broadcasting's turn again.
That's why recent heightened attention by public officials to the problem of TV violence and sex is welcome. Reed Hundt, chairman of the Federal Communications Commission, says he feels government has a constitutional right to enact a curb on violent programming. His rationale rests on a June court decision on indecent content that ruled the FCC can legally limit ''patently offensive'' depictions from 6 a.m. to 10 p.m.
Why not violence too, Mr. Hundt asks? He's not alone.
The Senate Commerce Committee has begun hearings on measures designed to control TV violence. President Clinton supports legislation requiring the so-called ''V-chip,'' a device attached to TV sets allowing parents to block violent programs. For the system to work, such programs must be transmitted with an identifying signal. That obviously worries broadcasters, because it calls for tough value judgments and would eat into viewership ratings - and ad revenues. So be it. The idea is promising because it would place additional viewing control where it is most needed: in the hands of parents.
Studies suggest that children daily witness 20 to 25 acts of violence during the hours they normally view TV - more than during adult prime time. Specialists have concluded that violence on TV can lead to violence in real life.
Many civil-liberties groups and most commercial broadcasters oppose government measures affecting content. But commercial stations occupy a special place in communications: They have use of publicly owned airwaves in the public interest - which legitimately includes protecting children from a daily diet of violence.
Regulatory steps are not, of course, the whole answer. Parental guidance and example are at the core of any move to keep children's upbringing focused on what's important in life.
One heartening development is the growth of ''media-education'' groups dedicated to making savvy viewers of both children and parents. But even savvy households need help.
Millions of parents, the president, and members of Congress are making a simple plea to broadcasters: Do something about the violence and debased values you shower on young viewers. If not, we have the power to do it for you.