The 2010 Prius Plug-In Hybrid Vehicle (PHV) made its North American debut on Wednesday at the 2009 Los Angeles Auto Show.

The Prius PHV has a first-generation lithium-ion battery. This is the same type of battery that powers laptop computers, and it allows more power to be packed into a smaller space. The newer battery will allow a Prius to drive in electric-only mode for longer distances and at higher speeds than a conventional Prius. You can recharge the battery by plugging it into a standard power outlet, otherwise the car reverts to standard hybrid operation using the gas engine as the primary motor. If your driving patterns are mostly short distances at lower speeds, a plug-in version of the Prius could dramatically increase fuel efficiency.

The arrival of a plug-in version of the Prius has been widely anticipated, and on Wednesday, Toyota made the official announcement that it was introducing a small number of these cars into the U.S. No word on when a larger rollout would occur.

Toyota has also launched a plug-in hybrid vehicle Web site on which consumers can follow the program’s progress and track the performance of the demonstration program vehicle fleet, it said in a statement

Toyota said the U.S. program will allow it to “gather real-world vehicle-use feedback to better understand customer expectations for plug-in technology. On the technical side, the program aims to confirm, in a wide variety of real-world applications, the overall performance of first-generation lithium-ion battery technology, while spurring development of public-access charging station infrastructure.”

Toyota is no doubt looking over its shoulder at the widely publicized Chevy Volt, a plug-in hybrid scheduled to be introduced late 2010. If the Prius brand is to retain its image as the most fuel efficient vehicle in America, it will have to adopt plug-in technology. Depending on the economy and the price of gas, expect to see these cars in dealerships in the second half of 2010.