Alcohol, long neglected at the gas pump and often abused at the bar, is gaining prominence as a motor fuel in the United States.

Politicians toast it as a weapon for "national energy security." Environmentalists tout it as a cure for dirty air. Farmers, who produce the grain from which most of today's alcohol fuel is derived, see it as money in the bank.

The alcohols used in fuels are of two basic varieties: ethyl alcohol, or ethanol, which comes from corn and other feedstocks, and methyl alcohol, or methanol, commonly obtained through the destructive distillation of wood.

The stuff is all the rage on Capitol Hill, where five bills have been introduced to increase alcohol use in motor fuels:A measure by Rep. Richard J. Durbin (D-Ill.) would require that 50 percent of all gasoline sold in America contain 10 percent ethanol by 1992. An identical bill has been introduced in the Senate by Sens. Paul Simon (D-Ill.) and Thomas A. Daschle (D-S.D.). A bill sponsored by Rep. James M. Jeffords (R-Vt.) calls for the replacement of 10 percent of U.S. gasoline with alcohol fuels by 1995. A proposal by Rep. Bill Alexander (D-Ark.) would amend the Clean Air Act to require that all gasolines sold in the United States after 1987 contain 10-percent ethanol or a comparable alcohol blend. Alexander's bill would also extend the 6-cent-a-gallon federal excise tax exemption for ethanol gasoline blends through the year 2000. The current exemption expires June 30, 1993. A measure by Rep. Dan Glickman (D-Kan.) would ease federal fuel economy standards for auto makers who produce fleets of "alternative-fuel-powered" vehicles. The government's Corporate Average Fuel Economy standards were put in place in 1978 to help reduce the consumption of gasoline in cars and light trucks.

Glickman's bill would help General Motors Corp. and Ford Motor Co., the nation's two biggest car companies, which are experimenting with vehicles powered by ethanol and methanol.

Alcohol was in vogue once before, during the oil crisis of the 1970s. But plunging oil prices killed most of that interest. Today, despite the talk of national security, the renewed attention to alcohol is sparked primarily by air pollution concerns, coupled with Farm Belt economics.

Some states, under pressure to meet federal air quality standards by the end of this year, are turning to alcohol to help reduce auto exhaust emissions. Supporters contend that alcohol fuels burn cleaner than gasoline, the combustion of which can produce harmful levels of carbon monoxide and other toxic substances.

Colorado earlier this month became the first state to require its big-city motorists to use ethanol-blended gasolines during the winter months, when smog is at its worst. The ethanol blends, commonly called gasohol, could reduce big-city carbon monoxide levels by up to 25 percent, according to officials of the Colorado Air Quality Control Commission. 1.

Formulas that require ethanol are very popular with farm state politicians, who sense that here might be the limitless market their constituents need to sop up all the excess grain that has been depressing prices.

In this context the surplus grain can be viewed, not as an economic burden, but as the key to energy independence.

However, to achieve the success their backers hope for, alcohol fuels will have to overcome major technical obstacles, the most important of which is economy. Not only is alcohol more expensive to produce than gasoline -- only tax breaks keep it competitive at the pump -- but cars that run on it get far worse mileage.

Ethanol gasoline blends get 15 to 20 percent fewer miles per gallon than those using straight gasoline. Those that run on straight methanol, still mostly experimental, do even worse. A fleet of methanol-fueled cars operated by Ford Motor Co. gets about 10 miles per gallon, about half the mileage those models get on gasoline.

In addition, alcohol, particularly methanol, can attack rubber and plastic engine components, leading to starting problems as well as leaks and possible fires.

Nonetheless, the renewed attention is heady stuff for an alcohol-fuels industry that seemed at death's door only a year or two ago.

"We made a lot of mistakes," said deLesseps S. Morrison, chairman of the New Orleans-based Louisiana Alcohol Fuels Corp., an ethanol producer. In earlier days, when profit potential seemed endless, excited businesspeople jumped into the alcohol fuels industry "with a total disregard for comprehensive planning," Morrison said.

Now, Morrison and other alcohol-fuels proponents say they are poised for a comeback. If so, even with the growth of legislative and regulatory support, they have a long way to go, according to a report published last week by the Department of Energy Office of Alcohol Fuels.

The competition from cheap gasoline forced alcohol-fuel producers to cut back prices and cut costs, the DOE report said. The competition also forced many of the distilleries to close, as many as 20 in 1986 alone.

Approximately half of the estimated 165 alcohol-fuel plants operating in the early 1980s remain in business today, according to DOE and other government figures.

Still, gasohol sales reached an estimated 805 million gallons last year, accounting for nearly 8 percent of total gasoline sales in 1986, "a slight increase from a year ago," the DOE report said.

Alcohol-fuels proponents say they are determined to boost that growth. And they are showing up in force on Capitol Hill in an effort to push through legislation that protects their interests and, they say, the strategic interests of the nation and the health and mobility of the American consumer.

Opponents of the legislation, largely composed of the nation's big oil companies, have also been lining up their troops. It is a conflict of odd alliances, with auto dealers and consumer groups joining the oil companies on one side, and with big auto makers and environmentalists joining alcohol-fuels lobbyists on the other.

Recent hearings on alcohol fuels in Colorado and on Capitol Hill are indicative of the struggle. Proponents, led by the Renewable Fuels Association, which represents the nation's ethanol manufacturers, argued in Washington that their product is winning increasing consumer acceptance despite the problems created by low gasoline prices.

"Over 450 billion miles have been driven on ethanol-blended fuels" since they went on the market in 1979, RFA president Eric Vaughn told the House subcommittee on energy and power. Most of those miles have been trouble free, and customer acceptance is rising steadily, he said.

Spokesmen for General Motors Corp. and Ford Motor Co. also like alcohol fuels. "A year and a half ago I told you that General Motors was bullish on methanol, and nothing has happened in the interim to change that position," said Richard L. Klimisch, executive director of GM's environmental activities staff.

However, Klimisch said that "many engineering refinements are necessary to commercialize methanol," which has higher corrosive properties than ethanol blends.

It is precisely because of those engineering problems that neither the federal nor the state governments should mandate the use of alcohol fuels, said oil industry and consumer group spokesmen.

"We believe it would be unwise policy for the federal government to tie the refining industry's hands by specifying a recipe for automotive fuel," said Urvan Sternfels, president of the Washington-based National Petroleum Refiners Association, which represents most of the nation's oil refiners.

Clarence M. Ditlow, executive director of the Center for Auto Safety, agreed with Sternfels' view. The rush to gasohol could lead to "disaster" for consumers, Ditlow said in comments in Washington and Colorado.

Alcohol-blended fuels tend to have higher volatility levels than all-petroleum gasolines, Ditlow said.

That means gasohol can become overpressurized and cause vehicle fires, and that it could cause "widespread driveability problems, including stalling."