LENA, Ill. — The sweet, musty reek of fermenting corn and pure alcohol hovers over the towering distillery here, one of a rising number of farmland factories turning food into fuel.

It sounds like the perfect answer to rising gas prices.

And indeed, ethanol is a growing business for Midwestern corn farmers, who can make more money growing an additive for gasoline than raising food for people and animals.

But even as corn-laden trucks rumble into the Adkins Energy LLC plant, and tanker trucks bearing the colorless liquid roll out, destined for gas stations, scientists have never fully settled the question of whether ethanol is a good business for the nation.

Some wonder if cars powered by a mix of gasoline and ethanol really spew fewer pollutants, as backers claim.

One Cornell University researcher argues it takes more energy to make ethanol than it gives off as fuel, creating a drain on the nation's energy supply, though that is a minority view. There is also the issue of its cost.

But the financial benefit to farmers from ethanol is substantial and its political appeal is undeniable, which is why the number of plants in operation will rise. There are 88 ethanol plants around the United States, and 16 more under construction. Industry observers expect 50 to 70 new plants to open by 2012.

In Hawai'i, there are three companies moving ahead with plans to produce ethanol locally. While most ethanol is made from corn, it can also be made from sugar cane, which is grown in the Islands.

Motivating the boom is President Bush, who signed a comprehensive energy bill in August requiring refiners to increase their use of ethanol from 4 billion gallons a day now to 7.5 billion by 2012. The cost will be at least $3 billion a year in government money given to the ethanol industry, a subsidy needed to make the price of ethanol competitive with gasoline.

"Nobody could buy ethanol without the subsidy," said David Sykuta, executive director of the Illinois Petroleum Council, which represents the state's oil refiners. "We have argued we could make a much cleaner fuel without it."

The government has propped up the ethanol industry for years, with advocates saying it cuts vehicle emissions when added to gasoline. Typically the blend at the pump is 10 percent ethanol, 90 percent gasoline.

One political attraction of ethanol is that represents a domestic substitute for imported petroleum. But no one asserts the United States could ever grow enough corn and distill enough ethanol to completely replace gasoline. Today ethanol makes up about 3.5 percent of the gasoline sold in the United States.

The primary interest in ethanol is centered in farm states like Iowa and Illinois, both large producers of both ethanol and corn.

Ethanol's supporters range from Decatur, Ill.-based giant Archer Daniels Midland, the nation's largest producer, to small family farms. Midwestern politicians are staunchly behind ethanol, which is seen as supporting the price of corn.

Beyond ethanol's political attraction, the environmental benefits are somewhat hazy.

Ethanol contains oxygen, which improves the efficiency of combustion in auto engines. This means tailpipe exhausts are fouled with less carbon monoxide, volatile organic compounds and other substances that create ozone, which aggravates lung disorders.

But ethanol is stained by one environmental drawback.

It increases the volatility of gasoline, meaning that in summer more gas evaporates from vehicles into the atmosphere. That actually worsens the ozone problem, although refiners reformulate their gasoline to minimize emissions.

Brian Urbaszewski, director of environmental health programs for the American Lung Association of Metropolitan Chicago, is unimpressed by the benefits of ethanol.

"If you used that reformulated gasoline without ethanol in the summer, there would be less ozone," Urbaszewski said.

Ethanol does reduce emissions from old cars that lack computerized engine management systems, but those vehicles are ever diminishing in numbers.

"It's questionable what kind of benefit you get from ethanol in the modern fleet," Urbaszewski said.

So is ethanol good or bad for the environment? "That's a real hard question to answer," Urbaszewski said. "The truth may be that it is a wash."

But Urbaszewski has no illusions that corn-belt politicians will ever drop their support for ethanol.

"It's a juggernaut that is impossible to stop," he said.