Fed policy makers make their decisions about interest rates behind closed doors, then communicate those decisions primarily through brief, cryptic statements that analysts busily decode in the days that follow.

But that kind of distance has become impossible in the two years since the American economy plunged into its worst financial crisis since the Great Depression. These days, Mr. Bernanke and the Fed have been bailing out financial institutions, printing money in unheard-of volumes and stepping in to fill the lending gap left by the crippled capital markets.

Even in better economic times, Mr. Bernanke, who was appointed by President George W. Bush in 2006, would be under pressure to get out the Fed’s message: his term as Fed chairman ends at the end of next January, and President Obama will have to decide in the next few months whether to nominate him for another term or replace him with his own choice.

The Fed has never wielded as much power as it does right now, but the very expansion of its mission has exposed it to more second-guessing and more challenges to its political independence than ever before.

“The Federal Reserve, in collaboration with the giant banks, has created the greatest financial crisis the world has ever seen,” Representative Ron Paul, Republican of Texas, said at a House hearing last week in which Mr. Bernanke testified about the state of the economy.

Republican lawmakers portray the Fed as the embodiment of heavy-handed big government, and have called for scaling back the central bank’s regulatory powers. But liberal Democrats, like Representative Dennis J. Kucinich of Ohio, have accused the Federal Reserve of caving in to demands by banks for huge bailouts, for failing to protect consumers against dangerous financial products and for being too secretive about its emergency rescue programs.

More than 250 lawmakers have signed a bill sponsored by Mr. Paul that would allow the Government Accountability Office to “audit” the Fed’s decisions on monetary policy  a move that Fed officials see as a direct threat to their political independence in carrying out their central mission of setting interest rates.