The Geo Metro, a tiny subcompact imported by General Motors Corp., is the leader of the pack when it comes to automobile gas mileage, according to a government survey of 1989 model cars.

For the third straight year, the Metro, made by Suzuki for GM's new Geo import division, led the Environmental Protection Agency's annual mileage list, averaging 53 miles per gallon in the city and 58 mpg on the highway.Imports dominated throughout the top of the list released Thursday, although a foreign car - the British Aston Martin - also posted the worst performance.

Three Aston Martin models, the Lagonda with automatic transmission and the Saloon-Vantage-Volante with both manual and automatic transmissions, averaged a paltry 8 mpg in the city and 11 mpg on the highway.

Buyers of poor-mileage cars, generally those vehicles that average less than 22 mpg, pay a gas-guzzler tax authorized under the Energy Tax Act of 1978 to discourage production and purchase of vehicles with poor fuel efficiency. So buyers of any of those Aston Martin cars would pay $3,850.

The top-mileage Metro has a 1-liter engine, three cylinders and a five-gear manual transmission. The other vehicles in the top seven were, in order:

-Honda Civic CRX, with a 1.5-liter engine, four cylinders and a five-gear manual transmission; 50 mpg city, 56 mpg highway.

-Geo Metro LSI, with a 1-liter engine, three cylinders and a five-gear manual transmission; 46 city, 50 highway.

-Honda Civic CRX HF, with a 1.5-liter engine, four cylinders and a five-gear manual transmission; 45 city, 52 highway.

-Ford Festiva, with a 1.3-liter engine, four cylinders and a five-gear manual transmission; 39 city, 43 highway.

-Daihatsu Charade, with a 1-liter engine, three cylinders and a five-gear manual transmission; 38 city, 42 highway.