U.S. automakers, who churned out boxy cars while pursuing fuel efficiency, are curving the sheet metal again in a bid to bring more customers back to dealer showrooms.

It is a kind of renaissance, a renewed emphasis on styling made possible by a mastery of fuel economy problems and a serendipitous decline in gasoline prices.

Car manufacturers now have more time to concentrate on aesthetics, according to domestic industry analysts, who say U.S. automakers apparently goofed by relying on look-alike "econoboxes" to help them through fuel-short, recessionary markets.

"The public got tired of those boxy little cars," said Steve Wancik, who tracks dealer sales for the McLean-based National Automobile Dealers Association.

"Good styling will sell a car before anything else, before price, before fuel economy, safety, anything. Styling ignites a little flame in the heart of the buyer," Wancik said.

He may have a point.

The only positive numbers on this year's domestic charts apply to sales of completely restyled, aerodynamic models, such as General Motors Corp.'s Chevrolet Camaros and Pontiac Firebirds, and to big cars and to luxury models, such as Ford Motor Co.'s Lincolns.

Foreign cars, particularly Japanese products, continued to do well, occupying about 28 percent of the domestic market as of Aug. 31. But domestic small cars took a beating.

For example, year-to-date sales (Jan. 1-Aug. 31) of GM's Chevrolet Chevette, long the company's mainstay in the subcompact market, were down 40 percent from the same period last year. By comparison, GM's Camaro sales were up 60 percent over a year ago, and Firebird sales were soaring 70 percent higher than last year's levels, according to industry figures.

GM practically begged customers to buy its 1982 Chevettes, thousands of which still are sitting in dealer showrooms. The company cut at least $400 from the Chevette's nearly $5,000 sticker price in an attempt to move the car.

But GM could hardly keep up with demand for its sleek new Camaros, with basic prices ranging from $7,630 to $9,700--depending on type. GM also is "busting its tail," according to one analyst, to meet demand for its even more expensive Firebirds.

"Pretty, new sheet metal will sell every time," said L. Ray Windecker, an auto industry analyst at Ford. He said buyers across all age and income lines will try to get their hands on a car with "attractively bent metal."

Ford is bringing out its own aerodynamic line, the Tempo, Topaz, Thunderbird, and Cougar, early next year. Company officials say their "all-new" cars will emphasize "form and function," using sculpted, wedge-shaped bodies to reduce wind drag and increase fuel efficiency.

"These cars will be unlike any we've ever produced," said J. J. (Jack) Telnack, Ford's executive director of North American design. The Ford wedges will be lined against GM's Camaros and Firebirds, and GM's pricey, redesigned Corvette--which has a body made of plastic, instead of sheet metal. But Telnack said Ford's major target next year is the foreign competition, which already has started testing the U.S. market with upper-priced wedges.

For example, Toyota has introduced its new Celica Supra (sticker price $15,685), Datsun has its 280 ZX ($15,000), Mazda is pushing its rotary-engine RX-7 ($13,220), and Mitsubishi, Japan's fourth-largest automaker, is entering the U.S. market on its own with a new line of cars led by the Starion ($15,000).

Mitsubishi currently does business in the United States through Chrysler Corp., which markets the Dodge Colt and Plymouth Champ, small cars exclusively produced for Chrysler by Mitsubishi. That arrangement will stay in place until 1990. But with its own network of 72 dealers in 22 U.S. cities, and with its own line of cars, Mitsubishi hopes to ensure its American presence and to shield itself from any ill economic winds that may, again, blow Chrysler's way.

Chrysler, the nation's third largest automaker, almost went bankrupt in 1979. But the company managed to save itself with government loans, aggressive cost-cutting, and a new line of mostly midsize cars. Chrysler's hottest sellers this year have been its luxury convertibles, with sticker prices ranging from around $13,000 to $15,000.

Is this a recession?

"It was," said J. D. Power, president of J. D. Power & Associates, a California-based firm that monitors consumer trends in the domestic auto industry. Power said many of the people who "sat on the sidelines" and did not buy cars during the recession were unemployed blue collar workers.

But he said there were other people -- employed, relatively affluent -- who yielded to the temptation of owning attractively designed products and bought a car. Those people, young professionals and what the industry calls "mature buyers" (people 55 and older), soon became the prime targets of domestic and foreign car designers, Power said.

Now that the recession appears to be ending, "Demand for new, attractive cars is being cut loose. . . . There will be enough variety in all of the cars out there to satisfy the tastes of many different consumers," Power said.

GM Chairman Roger B. Smith shares that optimism, perhaps too enthusiastically. Smith, whose company's overall car sales are down 13 percent from a year ago, believes U.S. new car and truck sales could reach an annual rate of 14 million units by the end of the 1983 model year.

The last time the U.S. auto industry turned in that kind of performance was in 1978, when domestic manufacturers sold 11.3 million passenger cars and 3.7 million trucks, according to figures compiled by Detroit-based Motor Vehicles Manufacturers Association of the United States Inc.

Smith said GM, which currently holds 43.8 percent of the domestic car market, will increase its share largely because of the company's $40 billion investment in new product programs.

Similar chants are coming from the corporate offices of Chrysler, Ford, and American Motors Corp. AMC's optimism revolves around its "all-new" 1983 model, the Alliance, which was designed by Renault -- AMC's French partner.

But all of the optimistic predictions could go up in smoke -- even if the U.S. economy improves substantially -- if the styling changes coming about in domestic cars prove to be skin-deep, said industry analyst James E. Harbour, president of Harbour & Associates in Berkley, Mich.

For example, he said the Japanese "are selling nearly every car that they can put in here because they have set a new standard for quality" that he said includes attractive styling and sound engineering.

"People aren't buying that quality because they're richer," Harbour said. "They're buying it because it lasts longer. If the domestic industry doesn't recognize that, it's going to go down the tubes."