DES MOINES, Iowa (AP) - Clean-burning ethanol may have a smoggy secret.

If power companies are to be believed, the only one way to keep up with the fast-growing ethanol industry is to invest in good old-fashioned coal-fired electricity. It's a line of logic that some say turns ethanol's clean-burning appeal on its head.

"It's just damning of the notion of ethanol as a clean fuel," said Mark Kresowik, a Sierra Club organizer based in Iowa. "If we need to burn coal to create a clean-burning fuel, we're not creating a clean-burning fuel. It rips the shiny green veneer right off of ethanol."

Coal is the old guard of energy production, generating about half of U.S. electricity. It is comparably cheap but much derided by environmentalists who note it is the nation's biggest source of the greenhouse gas carbon dioxide.

Ethanol is promoted as a fuel with the potential to wean Americans from foreign oil with the added benefit of reducing greenhouse emissions. It burns cleaner than gasoline and is made with renewable resources such as corn or cellulose.

All sides agree that it takes lots of electricity to produce ethanol. Utilities note a typical plant eats up as much energy as 1,600 farms.

The divide comes over where that electricity should come from. Environmental activists believe greener means, such as natural gas, should be used. Power companies argue that coal is the only cost-efficient solution.

In Iowa, the nation's top producer of corn and ethanol, dozens of plants are producing the fuel and more are being built. That has prompted a push for two coal-fired electricity plants, in Marshalltown and near Waterloo.

Both projects explicitly pitch ethanol as a reason for their construction.

"Coal really is the only cost efficient energy source for this industry," said Ryan Stensland, a spokesman for Alliant Energy Co., which would be a part owner of the Marshalltown plant. "You need the baseload energy, and there really are only three options: nuclear, which our country has decided not to pursue that path; natural gas, but it's just not economical; that leaves you with coal."

That argument makes sense - sort of, said Robert C. Brown, a professor and the director of the Bioeconomy Institute at Iowa State University.

Brown notes that the volatility of natural gas prices are a tough sell for utilities, even though the gas burns more cleanly than a typical coal-fueled plant. Still, he said it chips away at the image of ethanol as an environmentally preferable fuel.

"Certainly the public would expect a renewable fuel to be produced from mostly green, renewable sources," he said.

Many local residents and businesses support the proposed Iowa coal plants, each of which would cost $1 billion or more to build. But there also have been plenty of opponents. They raise environmental and health concerns as well as the irony of the situation.

"We've all been calling ethanol the green fuel of the future," said Nathaniel Baer, with the Iowa Environmental Council. "And we're talking about producing it with more coal power. It's just bizarre."

Governor Chet Culver has staked much of Iowa's economic future to production of ethanol, wind energy and other alternative power sources, and he has signed on with other governors to a plan aimed at reducing greenhouse gases. But asked about the incongruity of burning coal to produce ethanol, state officials declined to comment.

Instead, Roya Stanley, who directs Iowa's Office of Energy Independence, would only say the more study was needed and that greenhouse gas emissions needed to be reduced.

"In the end we want to close the loop, we want to be emissions neutral. I think that's always the goal," she said.