As the ever gas-conscious public shuns the fat Cadillacs, the big Buicks, the luxurious Lincolns and the cavernous Chryslers that often litter his lot, used car salesman George Brown, 53, has had to alter his pitch to survive.

In the last two months, he has only sold one car - a measly Mazda.

"Sure, you get more gas mileage from the little cars, but you got to go to the gas station all the time," says the paunchy, orange-haired six-footer, who favors white belts and matching shoes.

"Take that Cadillac," Brown goes on, beaming toward his sleek, silver 1976 Eldorado with a 25-gallon tank."It holds twice as much. Big cars get more range. Ever take a close look at a gas line? All you see are small cars."

Brown keeps talking: "And you've got to consider the comfort. You get in a little car and drive down to Atlantic City, it'll wear the hell out of you. The air conditioning probably won't work worth a damn because the engine's not big enough to pull it and . . ."

The pitch doesn't work these days.

Small gas-sippers are what the people are buying - at any price - if they are buying at all, a fact of gas-short life that accounts for the 70 percent drop in business at Brown's G & B Motors. "I used to sell a lot of Cadillacs," he says. "How there's no sense trying to buy 'em from the wholesalers. All they do is sit around."

As for the pint-sized used cars - the VWs, Datsuns, Mazdas and so forth - they are getting impossible to find as wholesalers charge near retail-level prices that allow small used car dealers like Brown little leeway for mark-up.

Every now and then, he might sell a pre-1974 full-sized American car that burns regualar. As for used cars that guzzle unleaded, says Brown, they fare no better than dinosaurs in the Ice Age.

"It comes down to one thing," he grouses. "If you've got the big cars, you're not going to be able to sell 'em. And if you're a dealer looking for small cars, you can't but 'em because the wholesaler's price is too high."

Just the other day, Brown was offered a 1973 AMC Gremlin, automatic. Six months ago, he could have picked it up for $400. Now, the wholesaler was asking $750, firm, "for a piece of junk!" scoffs Brown.

"Chrysler Imperials, New Yorkers, you couldn't sell 'em if you had 'em. The other day I could have picked up a Lincoln - a '75 see-dan - for 31 and a half, and it was loaded: power windows, doors, sears, am-fm radio, factory air, all the goodies."

Did he buy it? "Hell no."

The logic is easy to undestand if you take the 1976 Cadillac "see-dan" a man drove in recently. It had 33,000 miles, clean, $12,000 new, a peach. The driver begged Brown to steal it for $3,500. No dice, said Brown. "Who's gonna buy it from me?"

"Dealers are starving," he says. "You're out of business unless you've got small cars to sell."

So tough are the times, in fact, that Brown recently hunted down a Datsun B-210 for a customer off another lot and did not even get the usual $50 bird dog fee.

A "big car person" in a small car land, Brown is trying to adapt. Still, it galls him that a 1971 VW now fetches $1,350, a mere $500 less than a 1974 Cadillac Coupe de Ville. "It don't make any sense," he says. "Why would amyone buy a VW when they could spend the difference and ride in style and comfort?"

When The Pitch doesn't move the used Cadillacs, the Cutlasses and other assorted gas-snorters wearing out their welcome on his lot. Brown shifts into reverse and throws himself at the mercy of the buyers.

There comes a time, he says, when "you've got to be honest and give it away for $100 or $200 below what I've got in it. It's not good for a car to sit around. People might start wondering if there's something wrong with it. CAPTION: Picture, Large cars go begging on a Washington area lot, while small autos sell rapidly. By John Mcdonnell - The Washington Post