Laurel Centre is launching an experiment today. It will begin giving away free gasoline to encourage car pooling.

The Rte. 1 shopping center will give a gallon of gas for each member of a car pool who signs in between 10 a.m. and noon each Tuesday and then remains at the center for two hours.

"Car Pool" is defined as, "three or more adults from separate households in the same vehicle." If you own a van and bring along 11 guests, you get 12 gallons of gas free. You and two guests get three gallons.

As merchandising gimmicks go, this one makes more sense tnan most. If 12 shoppers can learn to travel in one vehicle instead of 12 vehicles, there will be lasting benefit for them, for the nation, and not so incidentally for Laurel Centre and its merchants.

What worries me is that the more successful an idea of this kind is, the more likely it is to stir competitors into even costlier giveaways. The urge to play "Can You Top This?" becomes irresistible, and when this kind of competition is carried to extremes, retail prices tend to rise.

Have you noticed what's being going on at local supermarkets? They are already off on another round of costly gimmicks.

The first freebie that came to my attention was advertised by A&P, which offered prizes of up to $1,000, with a total value of $400,000. Safeway immediately thundered back with $1 million in prizes. And in an attempt to avoid being left at the post, Grand Union bought a full-page ad in Sunday's Washington Post to announce its "Let's Go to the Races" game in which lucky shoppers can win up to $2,000 and a total of $213,200 in prizes. Other chains will be forced to offer similar gimmicks, and before long all the stores will be spending so much money in their attempts to steal business from each other that there will be no advantage to any of them.

It is naive to think that merchants who give away vast sums of money can do so without nudging up their retail prices. Somebody has to pay for those "free" games and prizes, and the indentity of that somebody is clear to all adults except those who still believe in Santa Claus and the Tooth Fairy.

Which reminds me: Did you see the op-ed column about cents-off coupons in Saturday's paper? Among other things, that column said:

Giant Food's suggestion that cents-off coupons be eliminated so that retail prices can be reduced is a "phony crusade." Giant Food is "so dominant in its market that it has little to gain from coupons." "Coupons are -- or could be -- a miniature bonanza for those who desperately need relief from inflation in the grocery store."

In addition, there was scorn for my view that there is no such thing as a free lunch: somewhere down the line the public pays for everything it is "given."

Pish tush, said the op-ed column. "The public doesn't pay the freight for coupon freebies; those who don't redeem coupons pay."

Last year, 81 billion coupons were issued. Only 3.4 billion were redeemed.

If the millions of people who chose not to redeem 77.6 billion coupons are not "the public," who is?

The op-ed economics maven argued that only the poor, who have more time than money, can afford to clip and save and file away coupons with the elaborate organizational care needed to bring them to checkout counters at exactly the same moment a sh opper arrives there with matching merchandise. The truth is that studies have indicated that the poor buy fewer newspapers and magazines and therefore have less access to coupons.

I had finished reading the column defending coupons when the housewife with whom I live sat down to breakfast. Our op-ed page was propped up on her reading stand.

When she got to the part about Giant being "so dominant" in this market, she looked across the table at me and adked, "Didn't I just read a business section article about how Giant had finally nosed out Safeway in the Washington area?"

"It appeared about a month ago," I said. "Giant now has about 33 percent of the grocery business in this area, Safeway has about 28 percent. Nationally, Safeway is much bigger, but in this area Giant has a slight lead."

She read on in silence for a while. Then I heard a whoop of disdain. "This man is in over his head," she said. "He doesn't know what he's talking about."

"Now what would cause you to say such an uncharitable thing?" I asked.

"He says all detergents are the same, so he buys the one that offers the biggest cents-off coupon. That shows you how much you men know about detergents, or about keeping house. Let met tell you a few things about detergents."

And she did. She was still telling me when I remembered that I had to get to work to start writing a column about gimmicks, giveaways, freebies, cents-off coupons, free lotteries, free prizes, and being taken for a free sleigh ride by Santa Claus.