The Federal Reserve will expand its program to replace short-term bonds with longer-term debt by $267 billion through the end of the year in a bid to reduce unemployment and protect the expansion.

The continuation of Operation Twist “should put downward pressure on longer-term interest rates and help to make broader financial conditions more accommodative,” the Federal Open Market Committee said today in a statement at the conclusion of a two-day meeting in Washington.

“Growth in employment has slowed in recent months, and theunemployment rate remains elevated,” the FOMC said. “Household spending appears to be rising at a somewhat slower pace than earlier in the year.”

Policy makers led by Chairman Ben S. Bernanke are taking steps to shore up the world’s largest economy as faltering growth leaves it vulnerable to fallout from the European debt crisis and looming fiscal tightening in the U.S. Payrolls expanded at the slowest pace in a year in May, and the jobless rate has been stuck above 8 percent since February 2009.

Policy makers left unchanged their view that economic conditions will probably warrant keeping interest rates“exceptionally low” at least through late 2014. The FOMC has kept the main interest rate in a range of zero to 0.25 percent since December 2008.