A diesel-powered Volkswagen Rabbit, getting an estimated 50 miles per gallon, topped official 1983 government mileage tests as imports, diesels and American-made cars with imported engines continued to dominate Environmental Protection Agency mileage ratings.

The Rabbit, made in Pennsylvania, has an imported diesel engine. Nine of the top 10 cars overall were diesels and, except for four different Rabbit models, all were imports.

The most fuel-efficient domestic cars were four versions of the Chevrolet Chevette and the essentially identical Pontiac 1000 with diesel engines made by Isuzu in Japan. They got 42 mpg with a manual transmission and 37 mpg with an automatic.

A 37 mpg rating was earned by two models of the new American Motors Corp. Renault Alliance. The car is assembled in Kenosha, Wis., but was designed and engineered by Renault, the French partner that controls AMC.

Rounding out the top 10 list of U.S-made high-mileage cars were four Dodge Omni and Plymouth Horizon models at 34 mpg with gasoline engines made by France's Peugeot.

Led by the 46-mpg Honda Civic, the 44-mpg Toyota Starlet, and the 40-mpg Nissan Sentra, Japanese imports took the first eight places overall in ratings of cars with gasoline engines, followed by the Renault Alliance.

The top U.S. cars with American engines included the gasoline-powered Chevette with manual transmission at 31 mpg, GM's Buick Skyhawk with gasoline engine and manual or automatic transmissions at 28 mpg and the manual Chevrolet Camaro at 26 mpg.

EPA ratings list only individual cars. The four U.S.-based companies say they are improving their corporate average fuel economy (CAFE) ratings, based on the average estimated mpg of all cars sold in the United States by each company.

GM and Ford are projecting a CAFE rating of about 26 mpg for their 1983 production. Chrysler officials believe they can reach 29 mpg. AMC, with the help of the Alliance, hopes for a fleet average of about 32 mpg.

EPA ratings no longer give separate city and highway mileage estimates, and EPA officials stress that the ratings are valuable for comparison shopping but do not necessarily reflect actual mileage a driver can expect. Many of the cars high in the ratings are special high-mileage models that score well in the tests but not in the showroom.

Volkswagen has topped fuel economy charts for six straight years, but high mileage has not helped VW's U.S. sales, which have fallen 40 percent in the last year.

Nor are the diesels that won eight of the first 10 places in the ratings doing as well on the market. Sales of diesel-powered cars have been hurt by lower gasoline prices and better fuel efficiency in gasoline engines.

Maserati's Quattroporte had the lowest overall rating at 8 mpg while Rolls-Royce's Camargue and Corniche were at 9 mpg. A Cadillac limousine was the worst domestic car at 10 mpg