In testimony Monday before the House Government Reform Committee, Richard S. Fuld Jr., the chief executive of Lehman Brothers, portrayed his company as mistaken in its assumptions about the health of the mortgage markets.

"With the benefit of hindsight, I can now say that I and many others were wrong," Mr. Fuld said in his testimony.

But he also said the failed investment bank was the victim of happenstance and financial markets that eroded too quickly for executives to contain the firm's losses.

On the same day Lehman Brothers was preparing to file for bankruptcy protection, the Federal Reserve Board eased collateral requirements for banks to allow more liquidity in the financial system, Mr. Fuld said in his testimony.

He also said that Lehman had unsuccessfully tried to become a bank holding company rather than an investment bank — a move the Fed allowed with Goldman Sachs Group Inc. and Morgan Stanley not long after Lehman's collapse.

"Had these changes been made sooner, they would have been extraordinarily helpful to Lehman Brothers," Mr. Fuld said.

He did not directly criticize the Fed for not offering Lehman a financial lifeline when its collapse was imminent, but he did say, "Had that decision been different, further dislocations in the markets might have been avoided."

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