Ford Motor Co. will begin phasing in automatic shift locks during the next several years, starting with its 1990 models, while General Motors Corp. is still studying them and Chrysler Corp. has no set timetable, according to reports.

Automatic shift locks prevent cars with automatic transmissions from being placed into gear unless the driver depresses the brake pedal first.The device, already in wide use by some import carmakers like Mercedes-Benz, Honda and Nissan, was developed by West German carmaker Audi in response to a lengthy federal investigation that concluded last month that drivers stepping on the gas instead of the brake pedal were largely to blame for unintended acceleration.

The National Highway Traffic Safety Administration also conclud-ed in its yearlong study that poor placement of the brake and gas pedals in some cars contributed to unintended acceleration, or the seemingly unexpected tendency for a vehicle to accelerate strongly and uncontrollably after being placed into gear.

GM is still studying the use of the devices in its cars and has made no decision on whether to use them, said Ward's Automotive Reports, a weekly industry newsletter. It quoted a Chrysler spokesman as saying the carmaker plans to introduce them but has no timetable because shift locks "are not something you just pull off the shelf."

Audi, which uses the device on all its models with automatic transmissions and has recalled about 250,000 older cars to retrofit them, is offering the shift lock technology free of charge to any carmaker.