WASHINGTON — The Federal Reserve is torn over when to slow its aggressive efforts to stimulate the economy.

Its uncertainty burst into view Wednesday, when Chairman Ben Bernanke testified to Congress in the morning and the Fed in the afternoon released the minutes of its last policy meeting. Stock prices gyrated through the day as investors struggled to determine whether the Fed might soon pull back — even gradually — on its extraordinary efforts.

The Fed is buying the bonds to try to ease long-term borrowing costs, encourage borrowing and accelerate growth.

WASHINGTON — Sales of previously occupied U.S. homes ticked up last month to the highest level in three and a half years, helped by a jump in the number of houses for sale.The National Association of Realtors said Wednesday that sales rose to a seasonally adjusted annual rate of 4.97 million, up from 4.94 million in March. Home sales have risen 9.7 percent in the past 12 months.