Most Americans prefer automatic transmissions. We have become, by and large, a shiftless society.

When Mercedes Benz introduced its much admired 300E a few years back, they ordered a 50-50 mix of automatics and 5-speeds. It was a miscalculation. Dealers ordered only 4 percent of these cars with a manual gearshift.Some experts say the demand for automatics, especially in expensive cars, is because it is very difficult to hold a car phone and shift gears at the same time.

Whatever the reason, virtually all top-of-the-line Mercedes, Jaguar, BMWs and Rolls Royces now come with automatics. A few models can be special ordered with 5-speeds, but most high rollers are not interested.

According to General Motors, most of us, regardless of income, are not really excited about manual transmissions. General Motors says 92 percent of the cars they sell are ordered with automatics.

The latest figures from the Environmental Protection Agency show that in nine out of 18 truck and car classifications, GM products with automatic transmissions obtain the best fuel economy. This speaks well of GM automatic transmissions, especially in the lower cost units.

However, this really should not come as any great surprise. Rolls Royce motorcars use an automatic transmission manufactured by General Motors.

Honors for best mileage by midsize cars goes to the Chevrolet Corsica with a highway reading of 31 and a combined figure (city-highway) of 26. Midsize wagons are led by the Pontiac 6000 and its GM sisters at Buick and Oldsmobile with a highway rating of 28 and 22 combined.

Large car honors go to the Pontiac Bonneville, along with the Oldsmobile 88 and Buick LeSabre, with highway figures of 28 and combined of 24.

The subcompact Geo Metro topped out at 39 on the highway and 37 combined. The Metro with a 5-speed topped all cars sold in the United States with 58 miles to the gallon on the highway. Metros are built in North America in a joint venture with Japan's Suzuki.

The Chevrolet S-10 pickup and its sibling the GMC Sonoma led their field with 28 highway and 24 combined. GM also got the best mileage in the 4-by-4 special purpose truck catagory and for standard 4-by-4 pickup trucks.

In one other category, cab chassis trucks, GM's Buick Coachbuilder Wagon came out on top.

There are other standouts. No. 1 in minicompact cars is Nissan's NX coupe. In the compact car classification there are the Isuzu Stylus, Hyundai Precis and Chrysler Eagle Summit, all getting a combined rating or 30.

The Honda Civic Wagon was best in the small wagon field with a combined rating of 29. Ford's Crown Victoria and Mercury's Grand Marquis headed the large wagons with a combined rating of 20.

The standard two-wheel-drive pickup classification went to Mazda. In two-wheel-drive special purpose trucks, the Chrysler Caravan and Voyager get the best mileage. Passenger vans went to the Toyota Pre-via, cargo vans to the Ford Aerostar and small four-wheel-drive pickups to the Ford Ranger.

To show just how far the automobile industry has come over the past decade, these following comparisons are made by General Motors.

The full-size 1991 Cadillac Fleetwood and Chevrolet Caprice return better fuel economy than the 1979 compact Chevrolet Nova. The 1991 mid-sized six-passenger Oldsmobile Cutlass Supreme sedan, equipped with a Quad-Four engine, gets better fuel economy than the 1979 subcompact Chevrolet Chevette.