Once more, President Bush has pushed ethanol as an alternative automobile fuel, to the delight of environmentalists, many people in the Midwest, and, naturally, the ethanol producers.

In his State of the Union address, he called for “investing in new methods of producing ethanol, using everything from wood chips, to grasses, to agricultural wastes.” He omitted the six-year time target he had set in last year’s address.

What exactly is ethanol? It is a colorless liquid also known as ethyl alcohol or grain alcohol and happens to be the ingredient that provides the kick in alcoholic drinks.

Corn kernels used to be a main raw material for making ethanol, but now the emphasis is on other types of “biomass,” such as corn husks and stalks, other plant fibers and industrial waste. In Old Town, for instance, one of the other companies that has signed on to the mill redevelopment project, Tamarack Energy, a renewable-energy developer, plans to first produce electricity to sell on the power grid, and eventually use equipment from the former mill’s pulp operation to produce ethanol.

Ethanol’s chief advantage as an alternate fuel or additive is that when produced from corn it can reduce the emissions that contribute to global warming by 20 percent compared with gasoline. Ethanol made from other fiber can cut those emissions by as much as 80 percent.

A downside is the expense. While ethanol usually costs slightly less than gasoline, its mileage is lower. A Chevy Silverado pickup truck, for example, gets 16 miles to the gallon of alcohol but only 12 miles per gallon of ethanol, according to U.S. News & World Report.

For Mainers, it’s still tough to buy ethanol. Any car or truck can burn up to a 10 percent mixture with gasoline, but it takes a $100 modification to burn “E85,” the 85 percent ethanol and 15 percent gasoline for the “flex-fuel” vehicles now being produced with federal subsidy by GM, Ford and Chrysler. But of the nation’s 1,026 service stations that sell the high-ethanol fuel, there is not a single one in Maine, New Hampshire or Vermont.

As a national cure-all for the U.S. dependence on Middle East oil, the focus on ethanol has stirred skepticism. The Financial Times quotes Adam Sieminski, a Deutche Bank analyst, as calling the development of the necessary technology “hugely expensive” and not achievable on an economic basis until 2015 at the earliest. The newspaper says that the International Energy Agency “calculates that the primary energy needed to generate a unit of ethanol is equal to 80 percent of the energy that unit of ethanol will produce.”

Bloomberg’s columnist Kevin Hasssett scoffs at charges that ethanol lowers our reliance on fossil fuels, helps clean the environment and will save the family farm. He quotes other researchers who added up ethanol’s total costs and found that it takes 29 percent more energy to make ethanol from corn than is contained in the ethanol itself. However, a study by the University of California at Berkeley concludes that using ethanol from corn produces 26 percent more energy than it takes to make it.

So don’t hold your breath for ethanol to solve our energy problem.