Sales of small cars - imports and subcompacts - during the first four months of this year were 34 percent higher than a year ago, while big car sales fell 16 percent, according to a survey by the Department of Transportation.

The still unreleased survey reveals that all manufacturers are experiencing record shortages of small cars.

Delivery time on new small cars is lagging as long as a year for the most popular models. The wait for a Volkswagen diesel Rabbit, for example, is now about a year, and some dealers are refusing to take orders for the car.

Other specific models also are doing well, the study reveals. Chevrolet's Chevette sales are nearly double those of the like period last year when the car was alreadly the best-selling domestic subcompact in history.

Dodge Omni and Plymouth Horizon models are selling at nearly double the rate of last year. And last week, Ford reported that sales of its beleaguered Pinto were running 22 percent higher than last year.

"People are willing to pay premiums for fuel-efficient cars," the DOT study states. "People are paying as much as $2,000 over the list price for the other cars."

The study also says that manufacturers and dealers are taking advantage of the situation by loading up their small cars with profitable options. Dealers convince customers to take the cars on the lot with the extra features because it will take too long to order the exact car they want, the study says.

The growing demand for small efficient cars has sharply affected the used-car market, the DOT study found.

"Small cars have depreciated mush less than large cars," it states. "For example, a 1975 Chevrolet Nova (V-8) (a compact) was selling in April for $2,550 - $50 more than a (full-size) 1975 LTD. And the LTD's initial price was $1,500 higher than the Nova's."

In general, the report noted, 1975 model compacts and subcompacts have depreciated about 25 percent, while full-size 1975 cars have depreciated about 50 percent.

The department is planning to release the small-car data officially today at a ceremony marking the delivery of two new, specially designed to protect occupants at crash speeds of up to 50 mph, and get at least 27.5 miles per gallon.

DOT's National Highway Traffic Safety Administrator, Joan Claybrook, has said the research vehicles prove "small cars don't have to be unsafe."

She said in a recent interview that if all the cars on the road were replaced by comparable vehicles from the DOT prototype program, 18,000 to 20,000 lives could be saved every year. CAPTION: Picture 1, Cars wait in line for gasoline outside Merit station at Sixth Street and Florida Avenue NE. The few stations that were open in the area yesterday attracted long lines of motorists. Photo by Margaret Thomas - The Washington Post; Picture 2, Bernice Tuppince and Daughter Jameise fill tank.