General Motors Corp.'s Chevrolet Cavalier, dubbed a product failure by many auto critics and buyers upon its introduction in 1981, now ranks as the top-selling passenger car in the United States.

GM sold 371,836 Cavaliers in the 1984-model year, which ended Sept. 30. That performance knocked Ford Motor Co.'s subcompact Escort out of No. 1 U.S. sales slot. Escort finished second with 339,209 unit sales for 1984, according to figures provided by Detroit-based Ward's Automotive Research.

No import finished in the top 10 in U.S. sales in 1984. The Nissan Sentra came closest, capturing the 13th slot with 192,000 unit sales. The Honda Civic finished in 16th place with sales of 161,000 cars.

Japanese imports would have done much better had they not been restricted by the "voluntary" quotas that have limited the shipment of Japanese passenger cars, vans and station wagons to the United States since April 1981, according to auto industry analyst Arvid Jouppi.

"But it is uncertain how much Cavalier sales benefitted from the quotas," Jouppi said. He said GM should be given credit for improving the Cavalier's styling and performance since its original, lackluster introduction.

For example, GM replaced the Cavalier's anemic 1.8 liter engine with a peppier 2-liter model. Some improvements in the car's suspension also were made. The estimated mileage rating for a four-cylinder model with electronic fuel injection and automatic transmission is 25 miles per gallon in the city and 30 mpg on the highway.

Ward's is predicting that the Cavalier will be the U.S. volume leader again in the 1985-model year with sales of 450,000 cars. However, Chevrolet spokesman Edward S. Lechtzin yesterday said his division expects to top the Ward's prediction by 50,000 units.

"Sales are a little soft right now because of the strike" by the United Auto Workers union that shut down 17 of GM's U.S. plants for one week last month, Lechtzin said. "But this car is selling across all age lines. We're getting young, affluent buyers as well as older buyers. We expect to sell 500,000 in the new model year," Lechtzin said.

The car's popularity will mean 1985 price increases of up to 4.2 percent over 1984 stickers, GM officials said yesterday.

For example, final 1984 sticker prices on the Cavalier ranged from $6,214 for a four-speed manual, four-cylinder, four-door sedan to $11,291 for a "fully loaded" Cavalier convertible. The list price spread on comparable 1985 models will range from $6,447 to $11,693.

However, GM officials said that the average price increase on their 1985 fleet will work out to about 2.3 percent, or $292 a car.

Other J cars include the Pontiac Sunbird (formerly the J-2000), Buick Skyhawk, Oldsmobile Firenza and Cadillac Cimarron.