The Fed’s chairman at the time, Ben S. Bernanke, was unusually clearsighted in warning of the risk of a severe recession as the nation entered into a presidential election year. But he struggled to persuade his colleagues, and at crucial junctures he did not push forcefully for stronger action.

The Fed’s current chairwoman, Janet L. Yellen, then the president of the Federal Reserve Bank of San Francisco, was even more alarmed by the deterioration of economic conditions. She and Eric Rosengren, president of the Federal Reserve Bank of Boston, are the most forceful and persistent advocates for stronger action in the transcripts. But they, too, underestimated the downturn until the final months of 2008.

The transcripts also show, however, that Fed officials responded decisively in those final months, probably preventing an even deeper recession. By the end of 2008, the Fed had reduced short-term interest rates nearly to zero for the first time since the Great Depression, and it had become a primary source of funding not just for the global financial system but for American homeowners and for companies that made food and cars.

Ms. Yellen summed up this new ethos at a Fed meeting six weeks after Lehman’s failure, telling colleagues, “Given the seriousness of the situation, I believe that we should put as much stimulus into the system as we can as soon as we can.”

In normal times, the Fed is a powerful but somnolent institution, charged with keeping a steady hand on the rudder of the economy. It moves interest rates up and down to moderate inflation and minimize unemployment. But beginning in 2007, it was forced to take on a far more challenging role as the central backstop for the global financial system.