As the economy recovers, banks may start lending out some of their hoards of reserves. That could lead to faster growth in broader money-supply measures and, eventually, to substantial inflation. But the Fed has the tools it needs to prevent that outcome.

For one, it can sell the large portfolio of mortgage-backed securities and other assets it has accumulated over the last couple of years. When the private purchasers of those assets paid up, they would drain reserves from the banking system.

And as a result of legislative changes in October 2008, the Fed has a new tool: it can pay interest on reserves. With short-term interest rates currently near zero, this tool has been largely irrelevant. But as the economy recovers and interest rates rise, the Fed can increase the interest rate it pays banks to hold reserves as well. Higher interest on reserves would discourage bank lending and prevent the huge expansion in the monetary base from becoming inflationary.

But will Mr. Bernanke and his colleagues make enough use of these instruments when needed? Most likely they will, but there are still several reasons for doubt.

First, a little bit of inflation might not be so bad. Mr. Bernanke and company could decide that letting prices rise and thereby reducing the real cost of borrowing might help stimulate a moribund economy. The trick is getting enough inflation to help the economy recover without losing control of the process. Fine-tuning is hard to do.

Second, the Fed could easily overestimate the economy’s potential growth. In light of the large fiscal imbalance over which Mr. Obama is presiding, it’s a good bet he will end up raising taxes for most Americans in coming years. Higher tax rates mean reduced work incentives and lower potential output. If the Fed fails to account for this change, it could try to promote more growth than the economy can sustain, causing inflation to rise.