If a child spends enough time watching "children's television shows," he's apt to learn something.

He'll learn he can't live without Teenage Mutant Ninja Turtles, brand-name shoes, the latest Nintendo game. . . . He'll learn he can't be cool if he doesn't eat a certain cereal. He'll learn about conspicuous consumption.At least, that seems to be the feeling in Congress. In an effort to put an end to what many claim is a trend toward program-long advertisements, lawmakers are expected to approve a children's television bill.

The bill would limit advertising on children's shows to 101/2 minutes an hour on weekends and 12 minutes an hour on weekdays.

The Bush administration opposes the bill, which it says could amount to violation of First Amendment rights. But the president hasn't said he'll veto the measure, which seems likely to pass. President Reagan exercised a pocket veto of similar legislation in 1988 - something Bush seems reluctant to do.

Reagan's administration had, in fact, backed the deregulation of the broadcast industry in 1984, heeding Federal Communications Commission arguments that a free marketplace is the best judge of what is in the public interest.

The legislation would also require the Federal Communications Commission to consider how well a state meets the educational needs of children when it is deciding to renew broadcast licenses. A station would have to show it meets education goals through its overall program, not just those shows designed specifically for children.

Opposition to the bill has been fading. The National Association of Broadcasters, initially concerned about freedom of speech issues, no longer opposes it.

It's too bad that such a measure seems necessary. But apparently the producers of children's television shows never have their appetites for advertising revenue sated.

While some of the items advertised are themselves educational and worthwhile, many of them aren't. Pity the poor parent who must try to keep up with his child's growing, television-fed appetites.