The joint action by central banks on Thursday to make it easier for weak European banks to borrow dollars is no doubt a policy nod in Mr. Posen’s direction, but it is still a far cry from the type of unified bond purchasing program, or quantitative easing, that he is advocating.

When Fed officials meet this week, they are widely expected to take further action to reduce long-term interest rates, a significant turnabout after months of suggesting that a recovery was solidly under way. The European Central Bank has not yet gone so far, but officials have recently signaled a new openness to reducing interest rates or at least to stop raising them.

In simplest terms, Mr. Posen wants central banks to print more money. A lot more money.

There is a certain tilting-at-windmills aspect to his crusade. The Fed will probably stop well short of the aggressive bond buying that Mr. Posen has advocated. Already, some Fed officials — and most Republican leaders, including the presidential hopefuls Rick Perry and Mitt Romney — believe that the Fed is at risk of rekindling inflation.

But that hasn’t stopped Mr. Posen from pressing his case. Earlier this month, he had lunch with Kiyohiko Nishimura, a deputy governor at the Bank of Japan, and Charles Evans, the president of the Federal Reserve Bank of Chicago. And, last Tuesday, he traveled to this small hamlet in southwest England to issue his most passionate cry yet ”I am here to warn policy makers in the United States, Europe, everywhere that we cannot take our foot off the pedal,” Mr. Posen said before a roomful of small-business leaders and bankers. “The outlook is grim — the right thing to do now is engage in more monetary stimulus.”

Although a few bubbles of sweat appeared on his forehead, Mr. Posen argued his brief here with aplomb — mixing self-deprecating remarks that touched on the oddity of a 44-year-old American prescribing monetary policy in Britain (“I get paid in pounds and pay rent in pounds,” he assured his audience) with a trenchant analysis of the economy’s various ills (stagnant growth, increasing unemployment and banks that will not lend).