In April 2012, Fed officials predicted that the benchmark rate would return to about 4.2 percent after the economy had recovered. In the Fed’s most recent predictions, in March, the average estimate was that the rate would reach 3.7 percent.

And some economists regard even those estimates as optimistic. Lawrence H. Summers, the former Treasury secretary, argues that the developed world may have entered a period of “secular stagnation” in which borrowing costs are unlikely to rise significantly above current levels because of chronic lack of demand.

John Williams, president of the Federal Reserve Bank of San Francisco, said in an interview this month that if Mr. Summers was correct, it might become necessary for the Fed to consider raising its 2 percent target.

“If you really thought that’s the world we’re in because of the demographics or productivity growth — if that’s really what our future holds — I think that’s just a reality that you need to think about monetary policy and its ability to achieve goals,” Mr. Williams said.

But Mr. Williams, like most central bankers, is not yet ready to do so.

He said the Fed had demonstrated in recent years that it retained considerable power to stimulate growth even after cutting rates nearly to zero through bond purchases and by announcing that it intended to keep rates near zero for an extended period.

David Lipton, the senior American official at the I.M.F., said recently that the crucial lesson was that central banks needed to take such measures more quickly. “It isn’t necessarily that you ought to be at 3 or 4, it’s that when you’re at 2 you’re just much more careful about preventing it from falling,” he said.

It is also possible that rates will increase more than the Fed expects, easing the pressure. Ben S. Bernanke, the former Fed chairman, has argued in response to Mr. Summers that rates are being suppressed by a “savings glut” in some countries, notably Germany, that is likely to dissipate as growth improves.