"If early and meaningful action is not taken, the U.S. economy could be seriously weakened," he told the Senate Budget Committee. Future generations, he said, will bear much of the cost.
It marked the Fed chief's most forceful warning to date on the potential problems facing the United States with the looming retirement of 78 million baby boomers, the oldest of whom will start retiring next year.
This huge wave of retirees will hit the U.S. budget in addition to the economy, Mr. Bernanke said.
"The longer we wait, the more severe, the more Draconian, the more difficult the objective - the adjustments are going to be. I think the right time to start is about 10 years ago," he told lawmakers when questioned about the urgency of the situation.
Absent policy changes by Congress and the White House, rising budget deficits are likely in the years ahead to increase the amount of federal debt outstanding to unprecedented levels, Mr. Bernanke said.
That could propel interest rates for consumers and businesses upward, which would be a worrisome development, he said.
"Thus a vicious cycle may develop in which large deficits lead to rapid growth in debt and interest payments, which in turn adds to subsequent deficits," he said.
Ultimately, a big expansion of the nation's debt "would spark a fiscal crisis, which could be addressed only by very sharp spending cuts or tax increases or both," Mr. Bernanke said.
The budget deficit last year totaled $248 billion, a four-year low. Mr. Bernanke noted the improvement but likened it to a "calm before the storm."
Spending on entitlement programs will begin to climb quickly during the next decade, he said. Federal spending for Social Security, Medicare and Medicaid will total about 15 percent of the gross domestic product by 2030, compared with roughly 8 percent of GDP in 2006, he said.
Forecasts call for the deficit to worsen for the 2007 budget year. The Congressional Budget Office is projecting $286 billion in red ink, while the White House is predicting an even bigger shortfall of $339 billion.
Mr. Bernanke said economic growth alone is unlikely to solve the nation's impending fiscal problems.
Fixing the problems, he said, will take persistence and a willingness by Congress and the White House to make difficult choices. It will be up to those policymakers to find the right balance between taxes and spending, he said.
The Fed chief steered away from offering any specific solutions.
Mr. Bernanke, who took over the Fed last February, made his case in somewhat starker terms than his predecessor, Alan Greenspan, who had repeatedly sounded the alarm about the dangers to the economy from exploding entitlement costs, some economists said.
"Bernanke didn't mince his words. He wasn't trying to candycoat the situation," said Brian Bethune, economist at Global Insight. "I think Greenspan was a little more diplomatic ... but at this point, a little more frankness is maybe what Congress needs."