WASHINGTON -- The federal budget outlook is worse -- much worse -- than you think.

U.S. Comptroller General David Walker on Thursday told the Senate Budget Committee that because of the huge mismatch between revenue and expenses, the budget picture "is not a pretty one, and it's getting worse."

"We need to recognize reality," he said.

The head of the non-partisan Government Accountability Office offered grim figures. The government's total liabilities and commitments to social insurance programs now total $50 trillion, about four times the nation's economic output. That's up from about $20 trillion in fiscal 2000.

The budget is on an "imprudent and unsustainable" path, partly because Congress has been cutting taxes since 2001 while dramatically increasing spending, Walker said.

In addition, the cost of the war in Iraq is growing, although he couldn't say by how much.

President Bush's tax cuts will not generate enough economic growth over time to compensate for any short-term revenue declines, he said. "We cannot grow our way out of this problem," he said. "The math just doesn't work."

Walker said Americans should not be comforted by the fact that in fiscal 2006, the budget's 12-month shortfall was just $248 billion, down from the previous year's $318 billion.

Even if Congress could continue whittling the annual deficit for the next several years, it would not be addressing the fundamental, long-term problem: It has promised more benefits to recipients of Social Security, Medicare and Medicaid than it can pay, he said.

He said Congress must fully fund Social Security and Medicare to absorb a "demographic tsunami" -- the more than 70 million aging baby boomers who will be retiring in waves beginning next year.

Walker's gloomy outlook was echoed by members of the committee. "We are facing a wall of debt," said Sen. Kent Conrad, D-N.D., the panel's chairman.

The budget imbalances are "simply staggering," said Sen. Judd Gregg, R-N.H.