(FORTUNE Magazine) – It's a Washington cliche that lawmakers will spend every available penny. But over the next few months, Congress will spend more money, more quickly, than anytime in history. Why the rush? The budget surplus is about to vanish. What the recent tax cut hasn't eaten up, the sluggish economy will soon devour. Adjust for a slowing GDP and a lower tax take, and "the surplus that remains available over the next ten years essentially disappears," says the respected Center on Budget and Policy Priorities.

The story only gets dicier: Congress has agreed to spend half of the $1 trillion surplus in the budget it passed earlier this year (a consideration not included in projections). And in the next few years, lawmakers will be forced to extend many of the multibillion-dollar breaks that were promised but not fully delivered in the tax cut. For instance, no one believes that legislators will allow the so-called death tax to be revived in 2011 (which is what the recent tax legislation calls for) after it's terminated in 2010.

You'd think some of these harbingers would worry Congress, but lawmakers seem unfazed. The only calculation that matters to legislators is the government's official--and predictably rosy--budget projection, which is decidedly in the black. For the next few months congressional estimates will peg the ten-year surplus at $1 trillion, even after walling off Social Security and Medicare.

In the meantime, the atmosphere in Washington resembles a grocery store before a snowstorm. In just one of the 13 annual appropriations bills this year, the House transportation subcommittee approved 900 projects--including $125,000 worth of sidewalks for a small town in Kentucky and $200,000 for a bike path in New Jersey--50% more than last year. "A very bad sign," says Tom Schatz, president of Citizens Against Government Waste.

President Bush isn't holding back either. Although he excoriated Congress for boosting discretionary spending for this fiscal year by 8%, to $637 billion, he's backing a measure that would add another $6.5 billion to that total, bringing the year-to-year increase in fiscal 2001 to 9.6%, three times the rate of inflation. Worse yet, an amendment to pay for this expansion with a tiny across-the-board cut in government spending was rejected by the House, 362-65. "The demand for additional spending is great and bipartisan," concludes Stan Collender, chief budget expert at Fleishman Hillard. Our bet: Watch for some serious buyer's remorse next year.