Foreign-made Rolls Royces, Aston Martins and Lamborghinis should not be exempted from meeting federal fuel economy standards for fleets of cars, a consumer group told President Carter in a letter yesterday.

The Center for Auto Safety wrote Carter to dispute recent actions by the Department of Transportation to set fleet fuel economy standards considerably lower for those cars than all others.

Although most auto companies must have 19 miles per gallon as an average for their 1979 fleets. DOT has proposed standards of 11 mpg for the Rolls Royce, the Aston Martin and the Lamborghini.

For 1980 cars, while the overall fleet averages must increase to 20 mpg. DOT has proposed no increase for Rolls Royce and a rise to 12 mpg for the other two.

In a fleet does not meet the standard set for it, it can be fined $50 per car for every mile per gallon it falls under the standard.

While such a fine could be devastating for price-sensitive cars like mid-sized American cars. "There is no reason why the millionaire who buys a $100,000 Rolls Royce should not have to pay a token $400 for the privilege of driving a gas guzzler," the center's letter stated.

Most of the American fleets have met the standard by introducing small cars to their lines to bring down the average. Cars like the Ford Fiesta and Chevrolet Chevette are used to balance out larger American gas guzzlers, although the companies have been scaling down even the larger cars to attain better mileage.

Government officials say the luxury cars marked for exemptions sell so few models it makes no difference, and fines of $350 or $400 per car mean little when they cost so much.

While Rolls Royce sells about 1,200 cars a year in the United States. Aston Martin sells only 250 and Lamborghini 120.

But center director Clarence Ditlow, in the letter to Carter, said the government, by granting exemptions to the rich, is endangering the support it has been getting from the general public, which has been willing to sacrifice the safety of heavier cars for lighter ones "because their improved fuel economy will lessen our dependence on foreign oil."

Ditlow called the relaxed standards for the expensive cars "insulting to Americans who are buying fuel-efficient compact cars."