IT'S THE END of an era, though we're not quite sure which one. The Federal Communications Commission on Wednesday abolished the requirement that citizen's band radio operators be licensed. This has not been the most heralded form of deregulation, since it's not clear that regulation kept people from operating their CBs on the wrong frequency anyway. Still, at the height of the CB radio fad in 1977, there were some 14 million licensed CB operators, and many more, perhaps 6 million, who were unlicensed. Now there are only 5 million licensed and perhaps 2 million unlicensed operators, and only about 30,000 applications arrive monthly --a drop in the bucket as far as the government is concerned, and not worth the cost of the paper work.

That cost, by the way, was not defrayed by license fees. At one time, a CB license cost $8, but for some years now it's been free because of a federal court decision. Under the paper napkin theory of economics, the lifting of the fee should have produced more license applications; as Jack Kemp might put it, when you make something free, you get more of it. But here, as elsewhere, pure free market economics has not explained how the world works: some things you just can't give away.

The FCC thinks that the reasons for the drop in the number of licenses are "boredom and fatigue." In other words, the novelty wore off. Maybe also people got used to the 55 m.p.h. speed limit, and weren't so interested any more in evading "Smokies"; the CB radio, though no one likes to say so out loud, has been used about as often as cigarette papers as a means to disobey laws several million Americans don't want to obey.

For whatever reasons, the CB craze, like the hula hoop craze, didn't last. There are lessons here for businessmen. Remember when the razzle-dazzle business writers were saying that student marketing was America's growth industry for the 1970s? Or when they said more recently that pizza parlors with video games and young people dressed up in mice costumes will help us meet competition from Japan? What these predictions miss is the fact that the businesses that respond to the latest craze often don't do all that well: they have a hard time tooling up to meet initial demand; their costs shoot up while they try to meet high demand; they keep producing as demand collapses. CB manufacturers and retailers got stuck with a lot of unsaleable 23- channel radios when the FCC allowed 40-channel sets. Regulators don't do better. The FCC, which hoped to prevent CB users from interfering with other frequencies, long ago gave up any enforcement program and admitted that it approved all license applications automatically. So the CB craze is now part of history, in the same chapter as the Canasta craze of the early 1950s, the hula hoop, and, we may hope, punk rock haircuts. Ten four.