AT&T is taking credit for the biggest investment yet by a U.S. company into a cleaner vehicle fleet, saying it will spend $565 million in the next decade to buy 15,000 alternative fuel vehicles.

And it looks like AT&T is planning to buy a significant number of the vehicles from Ford Motor Co., Reuters reported Wednesday.

The plan first calls for $350 million to buy about 8,000 compressed natural gas-fueled vehicles over the next five years. Corporate and government fleets are natural first adopters of CNG as a fuel, since they can supply their own fueling stations — AT&T plans to build 40 new fueling stations as part of its plan.

AT&T said only that it would look to “domestic suppliers� to convert van and truck chassis made by a U.S. automaker to run on natural gas. But Reuters reported that Ford is to build the chassis.

Ford may also be ahead in the lineup to supply AT&T with hybrid vehicles, as part of its plan to spend $215 million over the next decade to replace about 7,100 passenger cars with cleaner vehicles.

AT&T has been using four Escape hybrids in a pilot project in California since 2007, and Reuters reports that AT&T’s supply chain president said that Ford hybrids will make up most of the hybrids in an 800-vehicle trial run set for 2009. Toyota will also supply some hybrids, according to Reuters.

Ford has outlined plans for a more fuel-efficient fleet that will include an electric van in 2010 for fleet customers, leading to wider hybrid and all electric consumer vehicle offerings in 2012 (see Ford Outlines Fuel Economy, Electric Car Plans to Feds).

Back then Ford was asking for a $9 billion loan, but has since backed off, saying it is not in as dire financial condition as fellow U.S. automakers General Motors and Chrysler (see Hybrid-Electrics and Tough Times at Geneva Show).

AT&T’s decision to buy compressed natural gas vehicles earned it the praise of natural gas-and-wind power evangelist T. Boone Pickens, who has been pushing for adoption of the fuel as a way to reduce America’s dependence on oil imports (see Pickens Wants Natural Gas-Fueled Big Rigs).

“AT&T recognizes that our reliance on foreign oil is one of the greatest threats to our national security,� Pickens said in a prepared statement. “Hopefully others will follow their lead.�