By Hiawatha Bray, Globe Staff

Honda's new Insight is an odd-looking car, resembling a mutant Honda Civic. But the swoopy styling of the little coupe isn't nearly as adventurous as what lurks beneath the sheet metal.

For the Insight (www.honda2000.com/insight/) is a new kind of car, one that combines electric and gasoline power under the same hood. The Insight really is a mutant - or rather, a hybrid. And it'll be joined on the market next year by Toyota's entry, a five-passenger sedan called the Prius that's already sold 28,000 units in Japan.

Both of these cars take a clever approach to car design that promises lower fuel consumption and less air pollution, while delivering a car that the typical consumer would actually want to drive. ''It is a brand new technology on a brand new platform,'' says Mark Amstock, Toyota's national marketing manager for the Prius hybrid (www.toyota.com/afv/prius/intro_prius.html).

If all you want is a clean machine, you can go with an all-electric car powered by batteries. General Motors has been leasing its EV1 all-electric car (www.gmev.com) since 1997. But so far, only a few buyers have signed on. Consumers have rejected a car that has to be plugged into an electric socket every 60 miles, for a recharge that can take up to three hours.

So engineers decided on a different tack - a combination of electric and internal-combustion power, where each type of motor would help to overcome the deficiencies of the other. By adding an electric motor, a hybrid gets good acceleration without having to burn as much gasoline. By keeping a gasoline motor, the hybrid can keep its batteries fully charged at all times. It can also use a far smaller battery pack, weighing around 100 pounds instead of the 1,200 pounds of the all-electric EV1.

In a hybrid car, you'll find a small gasoline or diesel engine with a transaxle linking the power plant to the front wheels. So far, so ordinary.

But in the Toyota Prius, an electric motor and a generator are attached to the transmission. The generator, driven by the car's 58-horsepower gasoline motor, recharges the 135-pound battery pack, and can provide power for the 40-horsepower electric motor as well.

A sophisticated computer system constantly regulates the gas engine, electric motor and generator, using each in the most efficient way possible. Say you're pulling away from a stoplight. That requires lots of torque - the actual turning power delivered by an engine. As it happens, electric motors provide torque more efficiently than a gas engine. So the Prius will disengage the gas engine from the transmission and feed all its power to the electric generator. That power goes to the electric motor, which transmits it through the transaxle to the wheels.

But once the car is rolling along at a good clip, it's more efficient to rely on the gasoline engine for turning the wheels. The electric motor is shut off and the generator is used if the battery needs topping off.

Honda's Insight does it all a bit differently. The Insight has no generator, just an electric motor powered by a battery. Once again, the electric motor kicks in under those driving conditions that suit it best.

But how does the Insight recharge its battery without a generator? In fact, it does have a generator: the electric motor itself. Run an electric motor in reverse, and it generates electricity. So when the Insight is cruising, its electric motor can recharge the car's battery.

Both the Prius and the Insight take advantage of this principle at every stop light, in a technique called ''regenerative braking.'' Tap the brake, and the electric motor of the hybrid connects to the transmission. The motor runs in reverse, generating electricity and recharging the battery. Meanwhile, the car slows down as its forward momentum is used to spin the electric motor-turned-generator.

Regenerative braking is vital to a hybrid's efficiency. Traditional brakes just discard the energy of a car's momentum, turning it into waste heat. Hybrids still use traditional hydraulic brakes as well. But their regenerative braking systems let hybrids capture some of the car's lost momentum, then reuse it to get the car rolling again.

Hybrid cars still burn fossil fuel, just not as much as traditional cars. Toyota's Prius, somewhat larger than the company's Corolla compact sedans, gets about 55 miles per gallon. The Insight, a two-passenger coupe, should deliver more than 60 miles per gallon.

These fuel savings also mean a sharp reduction in greenhouse gas emissions. That's why Dan Becker is such a fan. Becker, director of the global warming and energy program for the Sierra Club, reckons that over its lifespan, a typical Ford Taurus sedan will dump 64 tons of carbon dioxide into the Earth's atmosphere. A Prius would contribute only 27 tons.

And unlike pure electric cars, the user of a hybrid doesn't have a rubber band on his bumper, dragging him back home every 60 miles or so to recharge his ride. With a hybrid, says Becker, ''You can do everything you want to do, anywhere you want to do it.''

Becker may be even happier in a few years, if scientists in Japan and the United States find ways to abandon gasoline for cleaner fuels. The ultimate goal is a car powered by a fuel cell; a system in which hydrogen and oxygen are mixed together in the presence of a chemical catalyst. The only byproducts of this reaction are water and electricity, so a fuel cell could be used to drive ultraclean electric cars.

But nobody expects to see fuel cell cars for another decade. Fuel is a big problem; to carry enough hydrogen, the gas must be stored under high pressure, in a big heavy steel tank that uses up much of the car's carrying capacity. Besides, there are no hydrogen filling stations on the nation's street corners. So for now, gasoline-powered hybrids are likely to be the energy-efficiency champs.

That's good news for the Japanese. Inspired by the high gas prices of their homeland, Japanese firms have taken a big lead in hybrid development, with American automakers lagging years behind. GM, Ford, and DaimlerChrysler have yet to announce when they'll start selling hybrids. But the Big Three have joined with the federal government in a research consortium that's developing hybrid technologies.

Thomas Kizer, director of powertrain and electrical engineering at DaimlerChrysler, said his company is focusing on mild hybrids, or ''mibrids.'' These will be cars and trucks where a traditional gasoline or diesel engine still does the great bulk of the work, using an electric motor only for the occasional assist.

''What we're looking for is the proper balance between the cost and the benefit,'' said Kizer.

Both Honda and Toyota think they've already found it. Soon we'll see if American consumers agree.

Hiawatha Bray is the Globe's technology reporter. His column, Upgrade, runs every Thursday in the Business section. His e-mail address is bray@globe.com.