``There is still a lot of development required before these vehicles are ready for prime time,'' David Hermance, executive engineer for Toyota's U.S. research unit, said in a speech in Sacramento today.

Hermance's comments show a growing divide among automakers about what technology will power a next generation of low- pollution automobiles. Toyota is betting that gasoline-electric hybrids are the more likely option, while Honda Motor Co. and General Motors Corp. have recently claimed significant advancements in making hydrogen fuel-cell vehicles for retail customers.

Engineers from Toyota, GM, Honda and DaimlerChrysler AG today briefed California officials on progress they're making readying ``zero-emission'' fuel-cell autos for sale. GM and Honda said earlier this month that they may put hundreds of the experimental autos into service across the U.S. over the next two years.

``I'm not quite as optimistic as'' the other automakers, Hermance said.

California, with air-pollution rules that exceed federal standards, reached agreement with automakers in 2003 requiring them to sell a small number of vehicles by late in the decade with no exhaust pollution. Most automakers have said hydrogen- powered vehicles are the best long-term replacement for gasoline- engine autos.

Fuel cells, typically layers of plastic, carbon fiber and precious metals such as platinum, create electricity in a chemical process that combines hydrogen and oxygen. Ideally, the only byproduct is water vapor.

Cost to produce the vehicles now exceeds $1 million, Honda and other automakers have said, and the U.S. lacks a network of hydrogen fuel stations to keep them running.