General Motors Corp. says it will cooperate with a government investigation of possible brake problems in 1.2 million of its cars but insists it's too early to draw conclusions.

The National Highway Traffic Safety Administration said the probe would cover the following models from the 1987 model year and part of 1988: Chevrolet Corsica, Pontiac Sunbird, Cadillac Cimarron, Buick Skyhawk, Oldsmobile Firenza, Pontiac Grand Am, Buick Skylark, Buick Somerset and Oldsmobile Cutlass Calais.The federal agency and GM have received 1,372 complaints of brakes not working unless excessive pressure is applied to the pedal, NHTSA spokesman Tim Hurd said. Consumers have blamed the problem for 189 accidents and 75 injuries, he said.

GM changed its braking system design, installing a new master cylinder and new formulation for brake pads, with the 1987 model year, Hurd said. It was changed again midway through the 1988 model year. The investigation covers the period between the two alterations.

The government is starting the probe as an engineering analysis, in which engineers study whether the parts in question have a safety defect.

The government also announced an engineering analysis of reports of slipping parking brake levers in the accidents. There are an estimated 69,775 of the cars on the road.

There have been 78 complaints of sticking throttles in the cars, of which 1.3 million are on the road. The problem has been blamed for six accidents and four injuries.