Aug. 24 (Bloomberg) -- Toyota Motor Corp., maker of the world's best-selling gasoline-electric car, says extensive U.S. consumer tests are needed before it offers hybrids that can be recharged at household outlets for limited all-electric driving.

``There is a consumer market at some price-point for plug- ins,'' Bill Reinert, national manager for advanced vehicle technology at Toyota's U.S. unit, said in an interview yesterday. ``We just don't yet know the size of that market.''

Toyota's caution reveals a difference in approach between the Japanese automaker, which has sold more than 800,000 Prius hybrids globally since 1997, and General Motors Corp., which wants to build as many of 60,000 Volt plug-in electric cars in the model's first year, people with knowledge of GM's plans said earlier this week.

Automakers are competing to develop fuel-efficient, low- emission vehicles as major markets tighten environmental rules and fuel prices rise. Plug-in hybrids that rely solely on electricity for limited distances would join gasoline-electric autos and hydrogen fuel-cell cars as possible alternatives to conventional internal-combustion power.

The Volt would theoretically travel about 40 miles after being charged at a household outlet. It would also have an on- board engine to generate electricity when the battery runs down.

Toyota plans road tests later this year of modified Priuses with rechargeable nickel-metal hydride batteries that allow about eight miles of all-electric range. Bob Lutz, vice chairman of Detroit-based GM, said this month that GM will test Volt prototypes with similar range by 2008.

California Tests

Toyota's U.S. tests, to be conducted at the University of California in Berkeley and Irvine, will be aimed at determining how easy plug-ins are to use, gather drivers' experiences with the cars, and measure how much they boost fuel economy.

``I know there's a lot of enthusiasm right now about plug- ins,'' Reinert said in the interview. ``I'm a little cautious about how much of that ends up as real consumer behavior.''

Plug-ins will probably be heavier than conventional autos, owing to the need for hundreds of pounds of batteries. Extra batteries to provide all-electric range could add between $5,000 and $10,000 to the cost of such a car, more than many consumers may be willing to pay, Reinert said.

The 2008 ``standard'' Prius is priced at $20,950. GM's 60,000-unit volume goal for the Volt could allow it to be priced at less than $30,000, said people with knowledge of the plans.

Low Awareness

The market for plug-in cars isn't clear ``because awareness is very low,'' said Scott Miller, chief executive officer of Synovate Motoresearch, a market research company in Royal Oak, Michigan. ``When people are educated, consideration is very high and exceeds that of regular hybrids.''

In a survey of 5,000 consumers conducted in December and January, about 10 percent said they'd be willing to pay ``substantial'' premiums for a plug-in hybrid once they understood the concept, Miller said.

When Toyota introduced the Prius in 1997, Miller said, it faced the same skepticism about affordability and technological hurdles.

``We can develop the best technology cars in the world, but society has to be ready to use them,'' Reinert said. ``We're going to see that real soon with plug-in vehicles.''

American depositary receipts for Toyota City, Japan-based Toyota rose $1.28 to $116.59 at 4:02 p.m. in New York Stock Exchange composite trading. They've fallen 13 percent this year. GM shares rose 30 cents to $31.05, and have gained 1.1 percent this year.

To contact the reporter on this story: Alan Ohnsman in Los Angeles at aohnsman@bloomberg.net

Last Updated: August 24, 2007 16:14 EDT