Board openings give Obama a rare chance to remake the Federal Reserve

"On a personal note, I would like to express my deep appreciation for Don's friendship and counsel during some very difficult times," Bernanke added.

The Fed is in particular need of PhD economists at its highest ranks. Bernanke would be the only economist on the Fed board if no new ones are in place before Kohn's departure. In addition to Tarullo, Fed governors include Bush appointees Kevin Warsh, a former investment banker, and Elizabeth Duke, a former commercial banker.

Newly appointed governors will probably have even more power than usual to influence economic policy. When the time comes to end the extreme support for growth, Fed leaders intend to use an unconventional tool -- raising the interest rate paid on bank reserves -- to pull money out of the economy.

Decisions on that rate are made by the board, not the Federal Open Market Committee, a bigger group that includes presidents of regional Fed banks and makes most monetary policy decisions.

"The stakes are now higher for new governors," said Vincent Reinhart, a former senior Fed staffer who is a resident scholar at the American Enterprise Institute.

At the moment, Fed officials are unified behind a policy of ultra-low interest rates to support the economy. But as the economy improves, some officials, especially presidents of regional Fed banks, are likely to be more eager than Bernanke to raise interest rates and drain the money supply, even at the risk of slowing the recovery. There are early signs of those pressures emerging, including a decision by Kansas City Fed President Thomas Hoenig to dissent at the last policymaking meeting, preferring not to promise to leave rates low for an "extended period."

New Obama appointees could push the center of gravity of the committee in the president's preferred direction. Fed watchers generally expect the president to favor appointees who would be in line with Bernanke's thinking or perhaps even more tilted toward worrying about unemployment as opposed to inflation.

Some liberal economists argue that the president should quickly appoint Fed governors who would be inclined to leave rates low for longer to try to get growth going again, even if it comes at the cost of mild inflation.

At the same time, an appointee who is viewed as too soft on inflation or too close to the administration could cause problems. If financial markets doubt the Fed's willingness to combat inflation, either because of appointees' economic views or because of a perception that they want to boost growth in the run-up to the presidential election, interest rates could rise. That would slow the economy.