When a farmer sows a field of corn in Iowa to meet the nation’s growing demand for the alternative fuel ethanol, is a corner of the Brazilian rain forest destroyed?

In the waning days of the Bush administration, a lobbying frenzy is now underway over the indirect impact this homegrown energy solution may have on land use around the world.

The ethanol industry is facing an Environmental Protection Agency analysis that apparently paints a bleak picture of ethanol’s role in climate change. Already this year ethanol has been blamed for high food and feed prices, for sucking up water, and for widening the dead zone in the Gulf of Mexico. The ethanol industry has strenuously disputed all of these claims. The EPA analysis attempts, for the first time, to measure the indirect global land impacts of biofuels — especially when rainforest and grassland are converted to cropland.

The wellspring of the debate is a Science magazine article published last February. The piece calculated that corn ethanol production causes nearly double the greenhouse gas emissions of plain petroleum gasoline, if the indirect global land impacts are taken into account. Specifically, the researchers noted that the world’s most important carbon dioxide-absorbing ecosystems — like the Brazilian rainforest — will increasingly have to be cleared for cropland to make up for the grain diverted from food production to ethanol production. Ultimately, the researchers concluded that corn ethanol isn’t worth the climate cost.

The EPA drew on the Science article’s modeling for its “lifecycle greenhouse gas emissions standard” — a proposed rule on how to measure ethanol’s impact on climate. The standard, ordered by Congress last December when it voted for a six-fold increase in U.S. renewable fuels production, was supposed to be published this month. Congress specified that the new ethanol had to have a positive impact on climate. The standard will ultimately be a major factor in determining EPA’s bottom line numbers comparing ethanol emissions to petroleum gasoline emissions.

But the proposed standard has been held up at the White House Office of Management and Budget for weeks. The OMB number-crunchers — the last stop in the federal rulemaking process — have had meetings with more than a dozen corporations, industry organizations, and environmental groups — all with sharply competing views on whether the EPA’s initial numbers on ethanol’s climate impact should be made public.

As these two meeting records show, among those weighing in with OMB have been corn ethanol industry leader Archer Daniels Midland; DuPont, which has several next-generation ethanol research projects underway; and General Motors, which earlier this year, before its financial woes deepened, made investments of undisclosed size in two advanced biofuels firms. The not-as-sympathetic to ethanol side include several environmental groups and the food industry, including Kraft, the American Meat Institute, and the Grocery Manufacturers of America — all three of which have blamed ethanol production for increasing food costs.

“Previous accountings of emissions for biofuels haven’t adequately considered that land is a scarce resource,” said Jeremy Martin, of the Union of Concerned Scientists, one of the experts who met with OMB. His is one of six environmental groups that have recommended the EPA data be made public so that it can be more fully debated.

But ethanol advocates argue there is no actual data showing that U.S. ethanol production promotes clearing of the Amazon Rainforest. Both the Science researchers and the EPA have relied on economic modeling and a variety of assumptions that could well be wrong, ethanol advocates say. The biotechnology industry has strongly advocated that the EPA not release any numbers comparing ethanol’s estimated greenhouse gas emissions to those of petroleum gasoline .

A bipartisan group of six senators from the heartland have weighed in with the same message, that the calculations are based on “incomplete science and inaccurate assumptions” and could place the entire renewable fuels program in jeopardy.

Paul Winters, a spokesman for the Biotechnology Industry Organization, said the proposed EPA rules appear to be in interagency review at OMB, meaning the departments of Agriculture and Energy are weighing in. That makes it ever more doubtful that the proposed rule will be released before December 20, which he said is viewed by many in Washington as the last likely date for new regulations in the Bush administration.

So the controversy may land in the lap of the Obama administration. There, the debate is likely to continue, as Nobel laureate Steven Chu, designee for Energy secretary, has been supportive of next-generation ethanol — ethanol produced from non-food crops like switchgrass and timber waste, for instance — but not ethanol made from corn. On the other side of the table, Senator Ken Salazar, Democrat of Colorado and Obama’s choice for Interior secretary, was one of the six senators who signed the letter supporting the ethanol industry’s view that the EPA analysis be withheld. And former Iowa Governor Tom Vilsack, who has been designated as secretary of Agriculture, has been a consistent supporter of biofuels.