WASHINGTON -- On the same day the Chevrolet Volt was unveiled in Detroit, a Toyota executive told a congressional committee that lawmakers would be wrong to enact tax credits that benefit only one plug-in hybrid design.

Robert Wimmer of Toyota did not identify the Volt by name. But he said pending legislation "redefines plug-in electric vehicles to seemingly eliminate consumer tax credits for all but one plug-in vehicle design."

He added: "Toyota believes this approach is counterproductive. It will discourage manufacturers from developing and consumers from purchasing 'blended' plug-ins that are affordable to the greatest number of consumers."

Wimmer is a national manager of energy and environmental research in the Washington office of Toyota Motor North America Inc.

The comments were part of prepared testimony for a hearing on progress with electric vehicles, held by the Senate Energy and Natural Resources Committee.

Wimmer referred to a tax package released by the Senate Finance Committee, which may be included in energy legislation that will be considered this month by the full Senate.

Toyota is experimenting with a new Prius hybrid, adding to its battery pack and making it capable of running longer in all-electric mode. A version of the vehicle is expected to be ready for fleet testing in 2010.

The Volt, scheduled to go on sale in late 2010, uses a battery pack rated at 16 kilowatt hours that is designed to run on all-electric power for about 40 miles. A small on-board gasoline engine is available to recharge batteries and extend range. The battery pack is larger than that of the existing Prius and the one being developed.

General Motors executives have warned that early Volts will be pricey -- subsidized in part by GM and, they hope, by hefty tax credits.

The Senate legislation would make tax credits available to plug-ins with at least 6 kilowatt-hours of electric power. Credits would reach $7,500 for light-duty vehicles.

Wimmer said: "We believe consumer incentives should encourage all plug-in designs and allow the consumer market to select winners, not legislation."

General Motors spokesman Greg Martin on Wednesday challenged the assertion that only the Volt would benefit from the proposed tax credit. He said Nissan, Mitsubishi and Tesla, as examples, have products or have indicated they will have products that might qualify.

He said it is understandable that Toyota's testimony "would reflect their competitive interests."