Japanese automakers have led the way in selling "hybrid" cars, which have improved fuel economy and reduced tailpipe emissions by running on either gasoline or electricity. But the Toyota Prius and Honda Insight, on the American market for a year, are costly to produce and sold in limited numbers at a loss. So Detroit is trying a middle ground, according to a Feb. 19 article by Keith Bradsher in The New York Times. American automakers will offer some "full hybrids," capable of running on battery power alone at low speeds, but are putting their main focus on electrically assisted gasoline engines. Such engines, which cost little more than conventional engines but use a less ambitious technology than some environmentalists want, will become an option or standard equipment on dozens of models in coming years, according to Bradsher. General Motors and Ford executives say they expect to offer various levels of electrically assisted engines at least as an option on most models, though in some cases it may take a decade or more. Other automakers are more cautious, but with GM and Ford together accounting for half the American market, their rivals are likely to follow suit. Despite a preference for full hybrids, environmentalists are mainly pleased by automakers' latest ideas. They are particularly surprised given that federal fuel-economy standards have been virtually unchanged since the late 1980's, and say the planned hybrids and voluntary pledges by GM and Ford to improve the gas mileage of sport utilities show that the industry is changing its ways. Auto executives say most of the vehicles are likely to be less fuel-efficient than the lightweight Insight coupe and Prius sedan, which get 48 to 65 miles a gallon. That high mileage, however, partly reflects their small, light bodies. Compared with gasoline-only models, Ford estimates that Detroit's more modest new hybrids can improve fuel economy by 10 to 20 percent, while the more ambitious designs, like those in the Insight and Prius, will gain up to 60 percent, according to Bradsher. The new approach will be to install electrical systems that are of lower voltage than for full hybrids and are recharged by the brakes. These will allow cars' gasoline engines to turn off automatically when a vehicle stops and turn on instantly when the driver's foot touches the accelerator, improving fuel economy and reducing emissions. Auto executives say lower-voltage hybrids offer many of the advantages of full hybrids at a small fraction of the cost. The new systems will also be able to run water pumps, power steering and heaters with less energy than is now required, and to provide extra acceleration when needed. But in contrast to the Insight's 144- volt system and the Prius's 274-volt system, the smaller systems, with 42 volts, are not powerful enough to provide much help in actually turning the wheels. Vehicles with these systems are becoming known as "mini-hybrids" or "mild hybrids."