It’s just one sentence – 14 words – out of a brief 281-word agriculture plank adopted unanimously by delegates to the Republican National Convention. To hear the howls from Midwest politicians, you would have thought the GOP was out to wreck the ethanol economy that’s getting blamed for a host of domestic and world woes.

Sen. John Thune, R-S.D., told the Associated Press that the ethanol plank is “a big mistake.”

“The U.S. government should end mandates for ethanol and let the free market work,” read the final sentence of an ever-so-brief GOP agriculture plank.

As Jerry Hagstrom, Capital Press Washington, D.C., correspondent, reported from the convention in St. Paul, Minn., those words may have hurt presidential candidate John McCain’s prospects in Farm Belt states.

But not so fast.

The Democratic National Convention’s adopted platform doesn’t even have an agriculture plank. It lumps farm policy together with statements on rural America, devoting a scant 189 words to both. In a separate energy plank, the Democrats pledge government investment in advanced biofuel production such as cellulosic ethanol.

That’s fuel-grade alcohol made from grass and wood instead of the near-sugar molecules from corn and soybeans that convert to fuel.

Three federal laws support ethanol fuels today. One is a tax credit – 51 cents a gallon for distillers. Another is a tariff – 54 cents a gallon on imported ethanol. The third is the 2007 energy bill mandating 36 billion gallons a year of ethanol mixed with gasoline within 14 years. Estimated ethanol production this year is 8.8 billion gallons.

A study by University of Missouri economists released in March 2007 predicts that despite government help, net returns on corn-based ethanol after next year “may be too low to result in significant further expansion of capacity.”

Biodiesel from soy oil shows negative returns starting in 2010. Baseline data in that study were assembled before grain prices went through the roof, driving up distilling costs.

Questions about biofuel break-evens go with those economic horror stories on what $5-a-bushel corn is doing to livestock feed budgets, and how $11.77-a-bushel soybeans distort global markets.

There’s a case for letting the fuels marketplace work.

However, as former Agriculture Secretary John Block told Hagstrom, government encouragement is needed today if alcohol-based fuels are to attain wide adoption in this country. A broad user base would set the scene for transition to cellulosic fuel production as the technology is moved from laboratory bench to economically feasible industrial production.

It’s something to think about.

The other thing to remember is that party platforms adopted every four years don’t mean all that much. After the campaign is over, Congress and the chief executive work their way through legislation by a different set of rules dictated by what’s politically possible.

Coalitions among trade associations and partisan makeup of the House and Senate will ultimately determine whether the government backs off its ethanol mandate.