Agents from the Federal Communications Commission proved they are serious about keeping dial-a-porn messages out of the hands of children when they slapped a California company with a $50,000 fine this week. It was one of the first such fines imposed by the FCC. There ought to be more of them.

As a result of the federal action, the company in question, Audio Enterprises Inc., Mill Valley, Calif., has gone out of business. The owners agreed with FCC demands to stop using interstate telephone lines to transmit obscene messages.In order to resume operations, the company would have to tone down the messages, and use access cards, credit cards, or scrambling devices to keep youngsters under 18 from dialing the toll line.

The FCC says the fine sends a message to other such operators, but how emphatic that message will be is debatable. The fine itself was not large, considering the California firm collected about $250,000 in revenues over a two-year period. Each year, the dial-a-porn industry produces about $54 million in earnings for providers and the phone companies.

The action by the FCC was not the result of comprehensive supervision of the dial-a-porn industry. It came about as the result of a complaint by a parent whose son and teen friends had run up a large phone bill listening to the messages.

This means, essentially, that private citizens must be the watchdogs to keep such obscenity out of the home and not hesitate to complain to phone companies and the FCC if children are exposed.

Simply protecting children is not enough. Such pornographic messages have no place in society, serve no interest, and may cause other problems. Earlier this year, Congress did the right thing and passed a sweeping law that totally bans obscene and indecent commercial messages.

That law is not presently being enforced because it is being challenged in lawsuits in New York and California. But for the sake of a decent and moral society it ought to be upheld and applied forcefully.