The National Highway Traffic Safety Administration is conducting a "preliminary evaluation" of consumer complaints about possible brake and engine defects that could involve 11 million cars made by General Motors Corp.

A preliminary evaluation is the first step in NHTSA's lengthy defects investigation process. It usually involves a request for any information the manufacturer might have related to a potential safety problem. The evaluations do not mean that a defect actually exists, and most end with no action against auto makers, NHTSA officials said.

The current evaluation was announced in NHTSA's monthly defects investigations report -- which also cites probes in various stages involving domestic and foreign auto makers and auto industry suppliers.

The GM evaluation focuses on the company's A, G, and F cars made for the 1978 through 1984 model years. That covers an estimated 9 million cars, an undetermined number of which might have brake backing plates subject to corrosion. A rusted plate could weaken and cause loss of rear braking power.

A cars include the Chevrolet Celebrity, Pontiac 600, Oldsmobile Cutlass Ciera and Buick Century. F models include Chevrolet Camaro and Pontiac Firebird. G cars are the Chevrolet Monte Carlo, Pontiac Bonneville and Grand Prix and Oldsmobile Cutlass Supreme.

NHTSA also is examining complaints affecting 2 million J cars made for the 1982 through 1985 model years. J models include Chevrolet Cavalier, Pontiac Sunbird, Oldsmobile Firenza, Buick Skyhawk and Cadillac Cimarron.

Some J models allegedly have engines that can surge, or accelerate without warning, causing possible loss of driver control, according to complaints made to NHTSA.

NHTSA also is looking at the possibility that some of GM's popular Pontiac Fieros -- 1984 models in this case -- may have defective tie rods, which link the cars' front wheels to the steering assembly.

GM officials said yesterday that NHTSA's request for information about the rusting brake backing plates stems from GM's recall in January of 63,865 A, G and F cars in Canada's maritime provinces.

The GM spokesman said his company received NHTSA's Fiero inquiry last week and is preparing a response to that agency request.