Economists and politicians have been raising the stakes on fiscal stimulus to keep the U.S. out of a severe recession.

And it's becoming a no-limit game.

What started as a modest idea a few months ago eventually grew into the hundreds of billions of dollars. Nobel Prize-winning economist Paul Krugman said in a recent New York Times column that a package on the order of $600 billion is needed.

In a 60 Minutes interview Sunday, President-elect Barack Obama said the consensus among economists is that "we're going to have to spend money now to stimulate the economy," and "we shouldn't worry about the deficit next year, or even the year after."

Federal Reserve Chairman Ben Bernanke has even gotten into the act, telling lawmakers last month that additional stimulus "seems appropriate."

Yet very quietly, the cavalry has already arrived in the form of a roughly $90-a-barrel drop in oil prices over the past four months, slashing costs on everything from gasoline and home heating to business energy expenses. That translates into as much as $300 billion in stimulus - more than 2% of gross domestic product - without lifting a finger or adding to the budget deficit.

"I'm amazed that not more is being made out of it," said Nariman Behravesh, chief U.S. economist at IHS Global Insight.

Behravesh's forecasting rule of thumb is that every 10-cent drop in gasoline prices is equal to a $12 billion tax cut - one that's aimed at lower- to middle-income households that pay a higher share of their incomes for energy. Businesses benefit, too, of course.

With gasoline prices now about $2 a gallon below their record highs, that translates into $250 billion to $300 billion for households and businesses, Behravesh said.

Chris Varvares, president of Macroeconomic Advisers, estimates the effect on consumers alone from the drop in energy prices at around $135 billion.

Mark Zandi, chief economist at Moody's Economy.com, estimates that if oil prices just stay under $75 a barrel - December crude settled just below $55 Monday - it's worth the equivalent of a $200 billion stimulus. If oil prices were to eventually fall to around $50 a barrel, hardly a farfetched notion, the stimulus would climb to $250 billion.

"It's not widely talked about," Zandi said, since "that benefit is getting overwhelmed by all the other costs" from the credit crunch and negative wealth effect on asset values.

Still, economic officials are missing out on a golden opportunity to talk up the economy's sole bright spot during the most critical spending season of the year, especially given that their policy actions seem aimed as much at improving psychology as anything else.

Though the drop in energy prices will likely stick, "it's happened so quickly it still hasn't sunk in people's minds," said Georgia State University forecaster Rajeev Dhawan, who pegs the stimulus at $200 billion for consumers and businesses.

It needs to sink in, and the sooner the better.

So maybe some of Treasury's TARP money would be better spent on full-page ads or mailers detailing how much lower energy prices are saving people each month.

Along with directions to the nearest mall.

(Brian Blackstone is a special writer at Dow Jones Newswires who covers the economy and the Federal Reserve.)

Copyright (c) 2008 Dow Jones & Company, Inc.