The Obama administration is proposing to lift the dollar cap on federal purchases of advanced technology vehicles so agencies can wean themselves off of gas guzzlers.

A provision in the proposed fiscal 2011 budget unveiled Monday would allow agencies to disregard price limits when purchasing commercially available vehicles that operate on emerging technologies — including electric, plug-in hybrid electric and hydrogen fuel cell vehicles.

The plan, which requires congressional approval, would "allow us to further enhance our efforts to green the fleet," said Stephen Leeds, acting administrator of the General Services Administration, which manages the government's motor vehicle fleet.

The price cap, which dates to at least the 1940s, is designed to prevent agencies from purchasing luxury cars. The current cap is $13,197 for sedans and $13,631 for station wagons. The caps can be exceeded by $3,700 for law enforcement vehicles and by $4,000 for special heavy-duty vehicles such as buses and ambulances.

Existing law already allows the caps to be exceeded by up to 5 percent for electric and hybrid vehicles purchased to further research and testing of new technologies, but that exception doesn't apply to alternative fuel vehicles that are already sold commercially. For example, the 2011 Chevrolet Volt — a plug-in electric hybrid from General Motors that is scheduled to go on sale in November — is expected to retail for about $40,000.

While the government has made good progress in greening its fleet, lifting the price cap would allow agencies to purchase some fuel-efficient vehicles that otherwise could be off limits, Leeds said.