WASHINGTON - The delicate task ahead for the Federal Reserve and other central banks is deciding when to start boosting interest rates and reeling in all the stimulus pumped out during the global financial crisis, Fed Chairman Ben Bernanke said Sunday.

Bernanke, however, didn't provide any new clues on that front.

As is typically the case in the early stages of an economic recovery, central bank officials "will have to weigh the risks of a premature exit against those of leaving expansionary policy in place for too long," Bernanke said in prepared remarks to a conference sponsored by the Bank of Korea in Seoul, South Korea.

The Fed's chief's remarks were prerecorded and delivered via video link.

Tightening credit too soon risks short-circuiting countries' economic recoveries. Waiting too long could risk unleashing inflation and sparking a dangerous new wave of speculation like the one that powered the housing boom and its devastating bust.

Because economic conditions vary country by country, the appropriate time to start tightening credit, varies, too, Bernanke said. "To guide these important decisions, each central bank will have to carefully monitor economic developments in its own jurisdiction," he said.

In the United States, the Fed has held a key interest rate at a record low near zero since December 2008.

Just last month, he repeated a pledge to hold rates at super-low levels for an "extended period" to nurture the fledging recovery.

Fears that a spreading debt crisis in Europe could hurt the U.S. recovery are prompting some economists to predict the Fed will be on the sidelines for longer than anticipated.

A growing number of economists now think the Fed will hold rates at record lows - well into next year, or perhaps into 2012. Just a month ago, many had thought the Fed would start raising rates near the end of this year.

Under the leadership of its new governor, Kim Choong-soo, the Bank of Korea last month also left its key interest rate at a record low of 2 percent.

Kim and other BOK policymakers must eventually decide when South Korea's economic recovery is strong enough to withstand higher borrowing costs.

Another challenge for central bank officials will be to make good use of the lessons learned during the global financial crisis, which hit its worst point in the fall of 2008, to sharpen its crisis-fighting tools, Bernanke said.

Countries, revamping financial regulations to better prevent another crisis, must work together to make sure the reforms are "consistent and coordinated across countries," Bernanke said. Congress is moving closer to a final package. On a global level, leaders of the Group of Twenty countries meet next month in Canada, where financial reform is a top issue.