ALL BUSINESS: Don't count on gas tax cut lowering prices

It's trickle down at its best ... until you drive over one of those super-sized potholes that jolts your car and rattles your teeth.

That's because the idea proposed by presidential candidates John McCain and Hillary Clinton to ease the federal gas tax would strip the U.S. government of about $10 billion for roadway and transportation projects.

And the plan doesn't even guarantee that lower taxes will lead to lower gas prices. Just the opposite might happen if the tax holiday spurs more demand for gas at a time when supply is already constricted.

It's basic economics. But it gets muddled when mixed with politics.

McCain and Clinton are trying to capitalize on motorists' dismay over gas prices topping $3.60 a gallon nationally. That's more than 20 percent higher than a year ago and it's hurting average Americans as they face mounting economic stress due to soaring food costs, fewer jobs, declining home prices and volatile financial markets.

McCain, the likely Republican presidential nominee, recommended the gas-tax moratorium during an April 15 speech where he laid out his economic plan. He called for cuts in the federal gas tax 18.4 cents a gallon for gas and 24.4 cents for diesel from Memorial Day to Labor Day the peak summer driving season. He also wants the United States to stop adding its emergency stockpile known as the Strategic Petroleum Reserve, a move that would lower the worldwide demand for oil.

Combined, he said, the two proposals would reduce gas prices, which would have a trickle-down effect. "Because the cost of gas affects the price of food, packaging, and just about everything else, these immediate steps will help to spread relief across the American economy," McCain said in the speech.

Clinton, who is still battling with Barack Obama for the Democratic Party nomination, announced her support of the tax holiday on Monday, and said she would make up for that lost revenue by imposing a windfall profit tax on oil companies. "I understand the American people need some relief," she said in an April 28 speech.

Before anyone starts counting on the potential savings, it's important to know that a gas tax moratorium might not give them much.