Why we buy what we buy - don't ask!

In case it escaped your notice, Parker is marketing a camouflaged pen - all black and green and khaki, just the thing for fading into the background of your tropical garden. We don't blame you if you have failed to take a bearing on the ''Camo,'' as it is known. If you're like us, you lose track of your pens even when they're not camouflaged.

What makes a ''Camo'' really hard to notice is that it blends into all those camouflaged jackets and pants, now the latest rage. Haute couture these days can look like something out of an Army surplus store. Young people are walking the city streets as if they're on duty in Southeast Asia.

''It's a jungle out there'' - and now we have the pen to prove it.

But we digress. The point we want to make more (with our very soft felt-tip) is that a pen is being sold for reasons having little to do with its writing quality. Oh, a passing reference is made to a ''roller ball cartridge.'' But most customers who buy the ''Camo'' are expected to make their purchase according to the same logic that prompts motorists to buy a car for its velour upholstery.

Such acquiring of useful objects for secondary reasons we have come to think of as the Crackerjack Complex. There may be some folks who buy the 11/4-ounce Crackerjack box solely for caramel popcorn and peanuts. But most people buy it with the ''prize in every box'' very much in mind. We recall one childhood friend who threw away the food to start with, getting right down to business.

This friend, we are convinced, would buy a ''Camo'' pen even if there were no ink in it.

There are TV channels, generally UHF, that sell, by mail or phone order, sets of knives or screwdrivers - at least to start with. Then the ''throw-ins'' begin. ''And that's not all,'' the announcer screams. ''We're throwing in a six-piece set of Tupperware....'' Bonus follows bonus. Tomato slicers and adjustable wrenches, salad choppers and keyhole saws flash, across the screen. ''And still, that's not all....''

By the time the spiel ends, the viewer has forgotten the product he was being sold originally. But he or she calls the 800-number in a panic, before the ''limited supply'' of whatever it is runs out - a case of the Crackerjack Complex.

If you are a Crackerjack Complex person, you will buy three pounds of hamburger because a package of buns is thrown in free - even though you don't like hamburger, least of all on a bun.

If you are a Crackerjack Complex person, you reserve airline tickets to Florida and California - the last places you may wish to go - just because the special rates are so low, and besides, you're getting a discount on your rental car.

To a sobering extent, we've all become Crackerjack Complex consumers. We start bank accounts, not because we prefer the services of a particular bank, but because it gives away cameras or umbrellas or potholders. We subscribe to magazines, lured by offers of a free digital watch or a world atlas or - why not? - both.

If we diverted customers have taken our eye off the product, so have the manufacturers. A Wall Street Journal survey indicates a ''brain drain'' of engineers from basic industries - automobiles, for instance - during the late ' 60s and '70s. It seems that stand-pat companies established a ''stifling environment'' for ambitious researchers who wanted to produce state-of-the-art designs. Did too much of the ''creativity'' go into TV ads - into selling the sizzle and forgetting the steak?

We'll probably buy a ''Camo'' anyway. We're pretty helpless at resisting any pen, for any reason.

The ''Camo'' may be a very good pen, too. The pity is, in the Age of Promo, where the excellence of a product is too often taken less seriously than the ''expertise'' of packaging and marketing, who's to know?