Stocks spiked after the Fed released the statement at the end of its two-day policy meeting. The Standard & Poor's 500 index and Dow Jones industrial average jumped to record highs. The Dow was up more than 100 points shortly after the statement was released.
In the statement, the Fed said that the economy is growing moderately and that some indicators of the job market have improved. But it noted that rising mortgage rates and government spending cuts are restraining growth.
The Fed repeated its plan to keep its key short-term rate near zero at least until unemployment falls to 6.5 percent from the current 7.3 percent. In the Fed's most recent forecast, unemployment could reach that level as soon as late 2014.
The Fed's short-term rate indirectly affects many consumer and business loans.
"We're in a slow-growth economy with high unemployment and low inflation," said Greg McBride, senior financial analyst at Bankrate.com. "There's no specific catalyst for the Fed to remove stimulus."
The Fed was widely expected to scale back its bond purchases. But long-term rates on mortgages and some other loans have jumped since May, when Bernanke first said the Fed might slow its bond buys later this year. Bernanke had cautioned that any reduction in purchases would hinge on the economy showing steady improvement.
At his news conference, Bernanke said there's "no fixed schedule" date or "magic number" for when the Fed will slow or end its bond purchases.
In its statement, the Fed said the rise in mortgage and some other loan rates in recent months "could slow the pace of improvement in the economy and labor market" if they're sustained.
Bernanke also said the Fed is concerned that looming fights between Congress and the White House over the budget and taxes could slow the economy. Unless Congress can agree to fund the government past Oct. 1, a government shutdown will occur.
The government is also expected to reach its borrowing limit next month. Unless Congress agrees to raise the limit, the government won't be able to pay all its bills.
"This is one of the risks we are looking at," Bernanke said.
The Fed lowered its economic growth forecasts for this year and next year slightly, likely reflecting its concerns about interest rates. It predicts that the economy will grow just 2 percent to 2.3 percent this year, down from its forecast in June of 2.3 percent to 2.6 percent growth.
Next year's economic growth will be a barely healthy 3 percent, the Fed predicts.
The Fed's policymakers expect the unemployment rate to fall to between 7.1 percent and 7.3 percent by the end of 2013, slightly below its June forecast of 7.2 percent to 7.3 percent. It predicts that unemployment will fall as low as 6.4 percent next year, down from 6.5 percent in its June forecast.
The Fed's policy statement was approved on a 9-1 vote. Esther George, president of the Federal Reserve Bank of Kansas City, dissented for the sixth time this year. She repeated her concerns that the bond purchases could fuel high inflation and financial instability.