One of those risks is a debt default by Greece, which could “roil financial markets globally,” including bonds and stocks, and potentially have a “quite significant” impact in the U.S., Bernanke told reporters at his second post-meeting press conference.

Stocks Break Rally
Stocks broke a four-day rally after Bernanke spoke and Fed governors and regional-bank presidents reduced their projections for economic growth and employment this year and next. The Standard & Poor's 500 Index fell 0.7 percent to 1,287.14. Yields on 10-year Treasuries were little changed at 2.98 percent, while the dollar strengthened 0.4 percent against the euro.

The U.S. economy grew at an annual rate of 1.8 percent in the first quarter, down from 3.1 percent in the fourth quarter, and recent data have shown manufacturing and consumer and business sentiment weakening.

“We don't have a precise read on why this slower pace of growth is persisting,” Bernanke said. Referring to “frustratingly” slow job growth and weakness in the financial and housing industries, Bernanke said “some of these headwinds may be stronger and more persistent than we thought.”

Jobless Rate Climbs
U.S. employers added 54,000 jobs in May, down from 232,000 in April, while the jobless rate climbed to 9.1 percent, the second straight increase after dropping 1 percentage point since November in the biggest four-month decline since 1984.

“The camel's nose is under the tent” for additional bond purchases, said Jason Schenker, president of Prestige Economics LLC in Austin, Texas. “Bernanke acknowledged a less-than-ideal recovery and left the door open for potentially more accommodation should it be required.”

Bernanke said that to further stimulate the economy the Fed could buy more bonds or cut the interest rate it pays banks on excess reserves held at the central bank. It could also pledge to hold interest rates at record lows for a longer period of time, he said.

Bernanke is keeping his options open on the Fed's next step, said Jerry Webman, chief economist and senior investment officer at OppenheimerFunds in New York.

'Wait and See'
“It's pretty clear that they don't see anything on the horizon that would get them to adjust policy one way or the other,” said Webman. “There has got to be a wait-and-see period to see what effects some of these temporary exogenous factors will have.”

The Fed in a unanimous decision yesterday left its benchmark interest rate in a range of zero to 0.25 percent, where it's been since December 2008.

Policy makers in a statement also repeated they will keep borrowing costs low “for an extended period” while tweaking the pledge to say it now depends on “low rates of resource utilization and a subdued outlook for inflation over the medium run.” That compares with previous language of “low rates of resource utilization, subdued inflation trends and stable inflation expectations.”

Bernanke said during the press conference that an “extended period” means the Fed would maintain rates at low levels for at least two or three meetings. The Fed meets eight times a year.

'Significantly Longer'
“The thrust of extended period is that we believe we're at least two or three meetings away from taking any further action,” he said. “And I emphasize at least. But depending on how the economy evolves, and inflation and unemployment, it could be, you know, significantly longer.”

While Bernanke and his Fed colleagues are predicting growth will pick up in the second half of this year, the slowdown in the first six months forced them to mark down their projection for all of 2011. They forecast that the rate of expansion won't exceed 2.9 percent this year, down from April's top-end forecast of 3.3 percent, based on the median range of projections.

“The language of the statement definitely opens the door” to another round of bond purchases by saying that inflation may fall below the rate deemed to be in line with the Fed's mandate from Congress, said Craig Dismuke, chief economic strategist at Vining Sparks IBG, a broker-dealer based in Memphis, Tennessee.

Inflation excluding food and energy prices will range from 1.5 percent to 1.8 percent this year, the Federal Open Market Committee said. That's higher than the 1.3 percent to 1.6 percent increase forecast in April.

Unemployment Forecasts
Policy makers also raised their forecast for unemployment, predicting it will average 8.6 percent to 8.9 percent in the fourth quarter of this year. That is an increase from the prediction of 8.4 percent to 8.7 percent in April.

At his press conference on April 27, Bernanke suggested that the hurdle for providing additional monetary stimulus would be high, saying the Fed had “done extraordinary things” to spur growth and that more stimulus may fuel inflation.

Policy makers at the April gathering focused on how and when they should begin withdrawing stimulus, according to minutes of the meeting.

Compared with his April news conference, Bernanke talked yesterday less about the threat of inflation and more about forces restraining growth. He mentioned the word “inflation” 71 times in April and 33 times yesterday.

Bloomberg News