WASHINGTON — Federal Reserve Chairman Ben Bernanke told a panel investigating the financial crisis that regulators must be ready to shutter the largest institutions if they threaten to bring down the financial system.

"If the crisis has a single lesson, it is that the too-big-to-fail problem must be solved," Bernanke said Thursday while testifying before the Financial Crisis Inquiry Commission.

Bernanke also said it was impossible for the Fed to rescue Lehman Brothers from bankruptcy in 2008 because the Wall Street firm lacked sufficient collateral to secure a loan.

Former Lehman CEO Richard S. Fuld Jr. told the panel a day earlier that the firm could have been saved, but regulators refused to provide help.

The Fed chief presented his analysis of the crisis and views on potential systemwide risks as the panel approaches the end of its yearlong investigation into the Wall Street meltdown.

The financial overhaul law enacted this summer gives regulators the authority to shut down firms when their collapse poses a broader threat to the system. The process resembles the one used by the Federal Deposit Insurance Corp. to close failing banks.

FDIC Chairman Sheila Bair told the panel "the stakes are high" for regulators to effectively exercise their new powers.

If not, "we will have forfeited this historic chance to put our financial system on a sounder and safer path in the future," Bair said. "The tools are there. The regulators have to use them," she testified.

Bair and Bernanke said tougher rules and market pressures will lead huge firms to voluntarily shrink themselves. Executives can no longer count on the government to bail them out if they veer toward failure, they said.

Bernanke said that bailing out these institutions is not a healthy solution and great improvement will come from the new law.

"Too-big-to-fail financial institutions were both a source ... of the crisis and among the primary impediments to policymakers' efforts to contain it," Bernanke said.

"We should not imagine ... that it is possible to prevent all crises," he said. "To achieve both sustained growth and stability, we need to provide a framework which promotes the appropriate mix of prudence, risk-taking and innovation in our financial system."

The Federal Reserve took extraordinary measures to inject hundreds of billions into the battered financial system during the recession. Last week Bernanke said the central bank is prepared to make a major new investment in government debt or mortgage securities if the economy worsened significantly.