WASHINGTON (AP) - The global rise in food prices is giving political ammunition to opponents of the country's ethanol policy and creating some uncertainty for the burgeoning and heavily subsidized biofuels industry.

An informal coalition of oil refiners, environmentalists and food processors is trying to convince lawmakers that increased output of the alternative fuel is inflating food costs by siphoning off corn otherwise fed to livestock and discouraging U.S. farmers from planting wheat, soybeans and other crops.

These strange bedfellows also argue that ethanol distribution constraints are contributing to higher prices at the pump, and that the biofuel is unlikely to reduce greenhouse gas emissions, and may even increase them.

Farmers and other ethanol supporters dispute these claims. But the lobbying blitz appears to be having some impact in Congress, and is putting shares of ethanol companies under pressure, a reflection of investors' concerns about the industry's long-term growth potential.

To help wean the country off oil imports, Congress has helped fertilize the country's budding biofuels industry with a 51 cent-per-gallon tax credit and a federal law mandating a five-fold increase in output over the next 15 years.

But twenty-four Republican senators, including presidential candidate Sen. John McCain from Arizona, last week sent a letter to the Environmental Protection Agency urging it to repeal or roll back ethanol output targets stipulated in energy legislation passed in December. And two weeks ago lawmakers tentatively agreed on a farm bill that would scale back the tax subsidy for corn ethanol to 45 cents a gallon.

"The political climate has radically shifted," said Matt Dempsey, a spokesman for Sen. James Inhofe, R-Okla., a staunch oil industry supporter and one of the senators asking the EPA to use the authority Congress gave it to halt the ethanol mandate.