Most normal American 8-year-olds have given more than a passing thought to the idea of copying a $10 bill. More than a few have tried it, but it is one of the great disappointments of childhood to learn that a copier isn't a money machine. The concept is right, but the end product, at this stage of the technology, isn't worth a plug nickel.

The Treasury is worried, though, about the future. As the state of the copying art improves and the machines are able to reproduce color and detail with greater fidelity, opportunities for counterfeiters will grow. By the end of the decade, say officials at the Bureau of Engraving and Printing, we're going to have a serious funny money problem.

In a news story published earlier this week, The New York Times revealed that the Treasury is considering various ways of printing money that will make duplication much more difficult. A multicolored pastel design on the edges of the bills would foil a copier. So would a thread placed vertically on the margin if it could be seen only when held to the light and not when the bill was placed on a flat surface. Our favorite option, though, is one that would coat the bill with a thin layer of film treated so that the picture would seem to shift in color or form as the bill is moved. When held in a certain light, for example, George Washington would appear to roll his eyes, or Abe Lincoln to lose and regrow his beard.

These are creative ideas but none quite matches a proposal around in the early '70s: pink C-notes. Forty percent of all the currency in circulation is in $100 bills. You may not see too many of them because, according to the Treasury, most of these bills are "underground," used by "those who seek a highly liquid, anonymous form of wealth, something that can be secreted in an ordinary envelop or stuffed in a suitcase. They include tax evaders, drug traffickers, illegal gamblers, loan sharks, fencers of stolen goods and corrupt politicians." Ten years ago, the Treasury considered making the $100 bills easier to spot by printing them in pink or making them too large to fit into a person's pocket. Officials also gave a thought to calling in large-denomination currency, forcing the underworld to deal in mountains of fives and tens.

Other countries use multi-colored currency, of course, and most of it is quite beautiful. Perhaps there are fuscha fives in our future, or dreams of mauve millions. That ought to stymie the copiers, too, for who could imagine a machine clever enough to calibrate the shades from aubergine to puce?