I'm standing in the checkout line at the supermarket when the guy at the register, who knows about this column, asks me a question. It's not a query that presses on the delicate membrane of the cosmos, but it is, in fact, a question I've been asked a lot lately and one I'm pondering myself.

"So," he says, as he weighs my apples, "should I buy a compact disc player or wait for DAT?"

DAT, as you may have heard, is digital audio tape, a relatively new method of reproducing sharply accurate, hiss-free music with the dynamic range of compact discs. DAT cassettes are only two-thirds the size of conventional ones, yet they hold up to two hours of audio.

This diminutive size makes it possible to build tape decks, Walkman-type stereos and auto stereos that are drastically smaller and lighter but capable of producing startlingly clear audio. CD players can't get smaller than the plastic discs themselves, of course, nor can tape decks or portables shrink smaller than conventional cassettes. DAT obviously wins the prize for digital music on the go.

So you probably thought I told the supermarket clerk to run right down to his neighborhood audio shop to buy DAT. I might have, but I couldn't. Although DAT machines and tapes are available in Japan, some powerful people think they're too good to be sold in the United States.

You read that right. According to the recorded- music industry -- whose lobby has been, forgive the pun, instrumental in keeping this revolutionary technology from being sold here -- DAT is just too good for American consumers. Here's why: Unlike compact discs, which are sold only in a prerecorded format, DAT cassettes can be used to play back or record. And there's the rub -- you can use a DAT machine to record other DAT cassettes or to make virtually identical dubs of compact discs.

That sends shivers through the board rooms and bank accounts of the recorded-music biz, which claims it already loses $1.5 billion annually because people make copies of records, tapes and CDs. Allowing DAT on the market, they say, would cut even deeper into industry profits -- maybe even put them out of business -- because unlike conventional tape, DAT reproduces music flawlessly.

Let's say you make a copy of a CD by recording it on your conventional tape deck. If you use a top-quality deck and equally good tape you probably won't be able to hear the difference between the CD and the copy. But if you dub the copy onto another cassette you'll lose quality, and you'll continue to muddy the sound with successive generations of copies. Similarly, you can dub a record onto a conventional cassette, but you'll add hiss.

None of this is true with DAT. Because it's digital, you can make unlimited DAT copies, and all of them will sound as sharp and hiss-free as the original. So the multibillion-dollar recorded-music industry has a modest proposal: Don't let DAT into the United States unless and until the CDs and DATs are copy-proof.

A research division of CBS has developed a spoiler system, for example -- one the recorded-music industry wants to adopt -- that would produce CDs and prerecorded DATs with a narrow band of frequencies deliberately left out. When used for copying, a DAT machine fitted with a special killer chip will detect the gap, automatically shut off and ruin the recording. Cute, huh? Only it's a manifestly stupid idea, one the Electronic Industries Association, the Consumer Federation of America and Consumers Union all oppose with good reason.

Using the CBS spoiler system (or anything similar) would be a giant step backward. There are electronics researchers around the world working to develop audio perfection -- crisp, lifelike sound reproduction -- and the recorded-music industry wants to purposely damage the quality of sound on compact discs and DAT to protect trade. That's like installing governors on cars to stop people from speeding.

Although some experts argue that the missing band of frequencies on CDs would not change the sound, others say its absence is noticeable on certain recordings and that it ultimately mutes, degrades and distorts CD sound. Besides, copy- protection schemes usually can be defeated by determined pirates -- so only the listening public loses in the end.

Next, look at the difference between piracy and copying at home. A pirate is a thief who sets up a warehouse operation with duplicating equipment to bootleg tapes and discs. Pirates are criminals, and they should be treated as such. But are consumers like me who occasionally copy CDs or records onto cassettes for use at home really in the same nefarious league?

Yes, says the recorded-music business, because I'm infringing on their property by home dubbing. Their property? The $15 I spent on a compact disc was just rent, and I don't really own it? The disc belongs to me, but the music belongs to them? And if I resell that CD to a used- record shop the way I sell used books, is that also an infringement?

In 1984, the Supreme Court ruled in the landmark Sony case that consumers could legally reproduce copyrighted works for "fair use," meaning noncommercial and personal use. The court ruled on videotaping, but there's no fundamental difference in the issue: If I buy a compact disc, why can't I dub it onto a cassette to play in my car or on my portable tape player just as I record movies off television? What's the harm? VCRs and home taping were supposed to beat Hollywood into the dirt, you'll recall, but they created a $5 billion industry instead.

Which leads me to think there's something fishy about this DAT business. Here we have a marvelous new source of digital sound, one that promises lower- priced, lightweight player-recorders, and the recorded-music industry wants it bottled up. Why? Not merely because it's concerned with piracy, but because holding back DAT for a few years gives the industry that much more time to milk the profits it's making from CDs' phenomenal sales.

Greedy? Sure, because the recording industry knows it will make billions from prerecorded DAT cassettes, that DAT won't kill off CD any more than compact discs bumped off conventional cassettes, and that DAT and CD will profitably coexist. Crippling digital reproduction with copy protection and entangling DAT in our trade problems with Japan is a lousy way to do business. Better to let American consumers make their own decisions about DAT instead of having their choices artificially limited. ::