TOYOTA is struggling to keep up with the booming demand for hybrid vehicles because it is unable to make enough batteries that are key parts in the hit "green" cars, a senior executive said yesterday.

The crunch on battery production is likely to stay for the rest of the year, as new lines can't be added to boost production until 2009, said Toyota Motor Corp Executive Vice President Takeshi Uchiyamada, who oversees production at Japan's top auto maker.

"Hybrids are selling so well we are doing all we can to increase production," he told The Associated Press.

Battery production is critical in determining how many hybrid vehicles Toyota can produce, Uchiyamada said at the company's Tokyo office.

Hybrids, including Toyota's top-seller Prius, offer better mileage than comparable regular cars by switching between a gas engine and an electric motor.

Toyota leads the world's auto makers in hybrids sold about 1.5 million units since coming out with the first mass-produced Prius about a decade ago.

Hybrids are soaring in popularity around the world amid surging gasoline prices, and other auto makers are also rushing to produce them. Hybrids also boast a green image in reducing emissions linked to global warming.

But Uchiyamada acknowledged such efforts hadn't yet extended to battery production because of the sheer problems in keeping up with demand.

"That has to settle down first," said Uchiyamada, who played a key role in the development of the Prius.

Toyota said last week its hybrid-battery joint venture with Matsushita Electric Industrial Co will begin producing next-generation lithium-ion batteries in 2009, and move into full-scale production in 2010.

Toyota also said it is to set up a battery research department later this month to develop an innovative battery that can outperform the lithium-ion battery.