They questioned, too, the Fed’s ability to stimulate the economy, an issue that is still at the center of the debate about its policies.

“There’s no guarantee whatsoever that this thing will do what we’re trying to do,” Donald Kohn, then the Fed’s vice chairman, said at a meeting later in August. As the Fed debated a strategy to encourage bank lending, he said, “I just think it’s worth giving it a try under the circumstances.”

But eventually, Mr. Bernanke and his colleagues concluded that they could see the future, that they did not like what they saw and that it was time to act.

“At the time of our last meeting, I held out hope that the financial turmoil would gradually ebb and the economy might escape without serious damage,” Janet L. Yellen, then president of the Federal Reserve Bank of San Francisco, said in December. “Subsequent developments have severely shaken that belief. The possibilities of a credit crunch developing and of the economy slipping into a recession seem all too real.”

The Fed’s eventual response, which it expanded significantly in 2008 and 2009, is now widely credited with preventing an even more catastrophic financial crisis and a deeper recession. It is not clear that quicker or stronger action in the fall of 2007 would have made a big difference. Critics focus instead on the Fed’s earlier failure to keep banks healthy and to prevent abusive mortgage lending, and on its later role in allowing the collapse of the investment bank Lehman Brothers.

“The outcome would have been different only if the Fed and others had reacted back in 2004, 2005, 2006” to curtail subprime mortgage lending, Mr. Poole, now a senior fellow at the libertarian Cato Institute, said on Friday in an interview on CNBC.