AGL Resources Inc. of Atlanta and San Diego-based Sempra Energy, which distribute natural gas, support the Pickens bill, which would give them new customers.

Dow of Midland, Michigan; Eastman Chemical Co. of Kingsport, Tennessee; and the American Forest and Paper Association, a trade group in Washington, were among 61 chemical and agricultural companies and trade groups signing a May letter that said "the speed of our increasing dependency upon natural gas" may raise costs and force "good U.S. manufacturing jobs to overseas competitors."

Representative John Sullivan, an Oklahoma Republican and a sponsor of the Pickens measure, said subsidies are justified given concern over oil imports and the 500,000 jobs the bill may create.

"I'm not a tax-and-spend liberal," Sullivan said in an interview. "This is something we must do."

$195,000 Truck

A long-haul truck that runs on natural gas can cost $195,000 to buy, about $100,000 more than the same vehicle powered by diesel fuel, according to Vaughn Jennings, a spokesman for Sullivan. The 8 million heavy-duty trucks in the U.S. consume about 2 million barrels of oil a day, about 10 percent of the nation's daily appetite for oil, he said.

About 112,000 natural-gas vehicles are on the road in the U.S., according to Natural Gas Vehicles for America. The bill will "jump-start the market," Richard Kolodziej, president of the Washington-based group, said in an interview.

'Billionaire Boondoggle'

The U.S. can't afford breaks for particular energy industries during a "debt crisis of massive proportions," said Kristy Campbell, a spokeswoman for the American Conservative Union, which advocates lower government spending, in an e-mail.

The Alexandria, Virginia-based organization called the bill a "T. Boone Pickens billionaire boondoggle" in a statement last month, and said any Republican senators who support the legislation risk getting a lower score on the group's ratings of conservatives.

Sullivan, who got a 100 percent rating from the group last year, said the conservative group backed a broader energy bill Republicans released in 2009 that included tax breaks for natural-gas vehicles, in addition to expanding oil production in places such as the Arctic National Wildlife Refuge.