WASHINGTON The boom in U.S. ethanol production that Detroit automakers and ethanol proponents have worked hand in hand for years to achieve could soon pit the two industries against each other over how much of the fuel in your vehicle's tank is too much.

With outlets for the alternative fuel growing slowly, the ethanol industry is considering asking federal officials to allow sales of gasoline with up to 20 percent ethanol, double the current limit, for use in all cars and trucks.

But U.S. automakers say outside of the 5 million vehicles they've sold that are capable of burning 85 percent ethanol, their cars and trucks weren't designed for such fuels.

General Motors Corp. Vice Chairman Bob Lutz, who touted ethanol's potential during this week's New York auto show, said he had asked GM's engineers last week about the effect E20 would have on its older vehicles.

"To put E20 in the fleet that's out there is going to corrode every non-ethanol fueling system," Lutz told the Detroit Free Press in an interview. "We absolutely guarantee the destruction of the engine and the fuel injection system if we go the E20 route. It will not work."

The push for E20 comes as the U.S. ethanol industry's supplies could soon outpace demand. The largest demand for ethanol comes from blending up to 10 percent ethanol into regular gasoline for cleaner emissions. Last year, ethanol producers sold 5.4 billion gallons, nearly all of which went into regular gasoline to replace now-banned blending chemicals. More than a dozen states either require 10 percent ethanol in gasoline or are debating such a standard.

The industry estimates its U.S. capacity soon will hit 12 billion gallons annually, thanks to ethanol plant construction and government subsidies. With Americans buying 140 billion gallons of gasoline a year, 10 percent ethanol blends likely will max out around 14 billion gallons.

Yet the industry and its backers in Congress are discussing far higher production targets; President George W. Bush has proposed 35 billion gallons of biofuels a year by 2017, most of which would be ethanol.

U.S. Sen. John Thune, R-S.D., told the Environmental Protection Agency last month that ethanol makers in his state were worried that "we will hit an E10 wall in the next two to three years if gasoline with a higher ratio of ethanol is not timely approved and made available to consumers."

"The need for fuel with a higher ratio of ethanol to gasoline is growing by the day," Thune said in his letter.

Sens. Jeff Bingaman, D-N.M., and Pete Domenici, R-N.M., the chairman and the ranking member of the Senate Energy and Natural Resources Committee, have introduced a bill targeting the production of 36 billion gallons of biofuels by 2022 and would require the Department of Energy to study E20 and E15 fuels. They're scheduled to present their bill at a hearing Thursday.

Some ethanol production will be soaked up by increased E85 sales, but they have been a minimal part of the market so far, due to a lack of fuel pumps and problems with transporting the fuel. A recent study by RL Polk & Co. found that of those 5 million E85-capable vehicles, 1.1 million were in California, Florida and Texas. California has one E85 filling station, Florida has fewer than five open to the public and Texas has 27, according to the National Ethanol Vehicle Coalition.

Most cars and trucks built after 1980 were designed to handle up to 10 percent ethanol after governments began allowing such blends following the oil crises of the 1970s. A 2002 study by the U.S. National Renewable Energy Laboratory found that vehicles made before 1995 might have trouble adapting to E20 and that E20 or similar fuels could cause emissions problems. Cars designed to use E85 have different fuel system parts that are more corrosion resistant, as higher ethanol blends tend to carry more water.

"E20 could create problems for consumers, and the use of E20 could result in voided warranties," said Charles Territo, spokesman for the Alliance of Automobile Manufacturers, the industry trade group that includes Detroit's automakers, Toyota Motor Co. and others. "We're all for the use of ethanol, but we need to make sure we aren't doing things that can have an adverse impact on performance."

(Distributed by McClatchy-Tribune Information Services.)