The top federal auto safety regulator has praised General Motors for working with Allstate Insurance Co. in a program to reduce comprehensive and collision insurance rates for buyers of the new GM X-body cars.

In a speech to an automotive maintenance and repair conference last week, National Highway Traffic Safety Administrator Joan Claybrook called the arrangement "a first for American insurance and industry."

Allstate had announced earlier that it would reduce insurance costs approximately 15 percent for collision coverage and 35 percent for comprehensive coverage X-body car owners because the two companies had worked together to develop the safety features of the cars.

"We believe that the damage confinement and repairability features built into the X-body cars will result in lower repair costs," said Allstate's vice president for claims, William P. Gregg. "Certain other features in the automotive design should have the effect of reducing theft."

Consequently, Gregg said, "Since claims on these cars should cost less than on cars without these design features, we will charge less to insure them."

Gregg said Allstate's subsidiary auto repair research center, Tech-Cor, contributed to the development of many of the "damage confinement and repairability features" of the new X-body cars - the Chevrolet Citation, Oldsmobile Omega, Buick Skylark and Pontiac Phoenix.

The safety features involved include safer bumpers, reinforced floor pans, protected steering assembly, eased serviceability, and the use of special alloy steels.

"We learned many years ago that the best way to improve motor vehicle safety is to design the original vehicle with those built-in features that work automatically to help avoid crashes or to limit injury when vehicles are inevitably involved in collisions," Claybrook said in discussing the GM-Allstate effort.

"It makes much more sense," she added, "to make vehicles with better brakes than to try to train 100 million drivers to drive safely with poor brakes. And it makes more sense to install safety glass and energy absorbing steering columns than to try to eliminate accidents altogether."

In an interview, Claybrook said she was "very pleased with the GM-Allstate arrangement . . . and I told GM so. They have done something here that long needed doing, and I only hope it is only the beginning."