A bunch of economists at the Department of Energy got out their calculators a while back and came up with statistical proof of something you already knew: Gas lines waste gas.

In the Washington area alone, according to the economists' formula, nearly one million gallons per month are burned in gasoline lines by cars idling or creeping forward a few feet per minute. If gas lines become an everyday part of life throughout the nation, the total monthly loss would exceed 100 million gallons -- slightly more than 1 percent of all the gas the nation uses in an average month.

Gasoline isn't the only thing idled away in gas lines, of course. The economists also tried to determine the dollar value of all the man-and-woman-hours spent in those idling cars waiting for a moment at the pumps.

The conclusion: In the Washington area alone, according to the formula, gas lines are costing a total of $1.9 million per month in lost time. If gas lines become a national phenomenon, the monthly cost would be about $200 million.

All these numbers are estimates, of course but they seem to be the best estimates available of how much waste is involved in the current gasoline situtation, where demand so greatly exceeds supply that in many urban areas drivers have to wait in line to get gas.

These numbers will be an important part of the debate next week when Congress takes up a new bill giving President Carter authority to impose gasoline rationing -- that is, to force demand down until it matches supply.

Six weeks ago, the House resoundingly defeated a standby rationing plan proposed by the president -- but that was before gas lines started spreading across the continent. Today congressional leaders beleive, rationing would win fairly easy House approval because the people are sick and tired of wasting time, money and gas in gas lines.

The Energy Department tried to quantify the waste to help Congree decide whether rationing would be less costly than waiting in line.

To determine the amount of gasoline wasted, the department relied on data gathered during the 1973-'74 shortage caused by the Arab oil embargo.

The researcher concluded that the average car made 5.7 trips to buy gasoline each month [a total of 69 per year] and the lines forced an average wait of 20 minutes for each purchase.

Using data from various studies, they concluded that the average car consumes about half a gallon for each hour idling time. They recognized that some engines are shut off while waiting in line, but found that starting a car anew uses at least as much gas as a minute's idling.

"Shutting off a car's engine will save gasoline." DOE said, "If the idling period is more than one minutes," but "It is likely that most vehicles in line will have to move at least once a minute."

All this produced a formula for determinig the wasted gas in any given region for any month due to gas lines: number of cars x 5.7 trips per car x .33 hours waiting time x .5 gallons idled away per hour.

In the Washington area, with just over one million households and an average of about one car per household the monthly waste comes to 950,000 gallons.

Applying this same formula to the national total of 103 million gas-burning cars, the researchers concluded that the waste of gas if every driver had to wait in lines would be more than 100 million gallons a month.

Determining the dollar value of time frittered away in gas lines was a tougher problem. Some of the motorists might be coporate lawyers who sell their time for $150 an hour, but others would be unemployed teengers whose time has no market value.

For a number conservative, simple and round, the economists guesstimated that the cost of all drivers' time would average out at $1 an hour. That was the basis of the conclusion that more than $200 million would be lost every month if gas lines become universal. CAPTION: Picture, Lines like this one on Bladensburg Road could cost millions in gas and time. By Larry Morris -- The Washington Post