General Motors Corp., seeking to burnish its environmental image, is set to announce today plans to begin production of fuel-efficient versions of its full-size pickup trucks and its city buses.

GM Vice Chairman Harry Pearce is scheduled to announce that the No. 1 auto maker plans within the next few years to begin selling so-called "hybrid" variants of its full-size pickups, in which an electric motor assists the gasoline engine, improving the truck's fuel economy, a GM official familiar with the matter said.

Mr. Pearce also is expected to say that, later this year, GM will start delivering hybrid-powered buses in which the diesel engines are augmented by electric motors.

GM's proposed announcement that it will move both hybrid vehicles from testing to production comes just days after Ford Motor Co. sought to steal the auto industry's environmental mantle by pledging to improve the fuel economy of its sport-utility vehicle lineup by 25% over five years. Together, the Ford and GM announcements show that the auto industry is shifting its environmental focus from cars to light trucks - the SUVs, pickups and minivans that are proving increasingly popular with consumers.

Mr. Pearce also plans to outline other technologies GM is working on to improve the environmental performance of its vehicles over the next five years. The announcement is intended to demonstrate that the company is "the fuel-economy leader and will be the fuel-economy leader within five years," the GM official said.

A demonstration fleet of about 15 hybrid-powered GM full-size pickups hits the road this year in California, New York and three other states. In addition, GM had a hybrid-powered bus on the streets of New York from late last year to early this year; that bus now is being analyzed in preparation for larger-scale production.

Ford said it would achieve its SUV fuel-economy gains largely through technologies it has been working on for years - advances such as lighter-weight materials and more-efficient engines and transmissions.