Ben S. Bernanke stepped into the imposing two-story marble atrium at the U.S. Federal

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Reserve’s headquarters and took the oath of office from his deputy. The president lauded Mr. Bernanke as ‘‘an economist’s economist’’ who had ‘‘earned the respect of the global financial community.’’ A cabinet secretary, members of Congress and two former Fed chairmen looked on.

That was then.

This is now. Mr. Bernanke was sworn in Wednesday to a second four-year term as chairman of the central bank in a quiet ceremony that had none of the pomp and praise of four years ago.

Back then, on Feb. 6, 2006, unemployment was 4.8 percent and the Fed had just raised its benchmark interest rate to 4.5 percent as it tried to slow the economy and prevent inflation. The Senate had confirmedMr. Bernanke by acclaim.

The Fed’s institutional prestige was so high thatGeorge W. Bush paid a rare visit— only the third president to do so.

Today, the unemployment rate is 10 percent, and the Fed has kept the federal funds rate, its main policy lever, near zero for more than a year as Mr.

Bernanke and the bank have been criticized for contributing to the housing bubble and the financial collapse.

The Senate reconfirmed Mr.

Bernanke on Jan. 28 by the narrowest margin in the Fed’s 96-year history, and only after lobbying by the White House.

Neither President Barack Obama nor any other top official attended the ceremony held Wednesday in the same atrium in the Marriner S. Eccles Federal Reserve Board Building, named for a former chairman. It was restricted to staff members, although Mr.

Bernanke’s wife, Anna, was present.

After the Fed’s vice chairman, Donald L. Kohn, administered the oath, Mr.

Bernanke told employees that he had begun his second term ‘‘with considerable gratitude and not a little humility,’’ according to a 717-word statement supplied by the Fed.

‘‘At the Federal Reserve and other agencies, the crisis revealed weaknesses and gaps in the regulation and supervision of financial institutions and financial markets,’’ Mr. Bernanke said.

The Fed, he said, was revamping how it conducted oversight and was collaborating with Congress and the financial authorities in other countries to reform banking regulations.

However, Mr. Bernanke also defended the Fed’s autonomy, at a time when some critics in Congress have called for auditing its monetary policy.

‘‘Institutional independence brings with it fundamental obligations of transparency, responsiveness and accountability,’’ Mr. Bernanke said, adding: ‘‘It is essential that the public have the information it needs to understand and be assured of the integrity of all our operations, including all aspects of our balance sheet and our financial controls.’’ Earlier Wednesday, Kevin M. Warsh, another Fed governor, suggested in a speech in New York that the regulatory debate in Congress was not addressing the right questions.

‘‘Policy makers, inmyview, should be more focused on what constitutes effective prudential supervision, rather than be diverted to the less consequential discussion as to who should perform it,’’ Mr. Warsh told the New York Association for Business Economics.

He said the idea of ‘‘resolution authority’’— whichwouldempower a regulator to step in and dismantle a failing financial institution before it jeopardized the economy — ‘‘is unlikely, in the near term, to drive the market discipline required to avoid the recurrence of financial crises.’’ He called for more accurate and timely information to be provided to shareholders, creditors and regulators; more robust competition in the financial services industry, which he described as ‘‘ripe for a healthy dose of creative destruction’’; and stronger capital and liquidity requirements, along with better corporate governance and risk management.

‘‘We need a new financial architecture, one in which improved regulation and supervision play an important but coextensive role with greater market discipline,’’ he said.