WASHINGTON – More Americans unexpectedly signed contracts in February to buy previously owned homes, signaling government efforts to support the market will start pay off.

The index of purchase agreements, or pending home sales, rose 8.2 percent, the second-biggest gain on record and the largest since October 2001, after a revised 7.8 percent drop in January, the National Association of Realtors announced Monday in Washington.

Buyers may be vying to take advantage of an Obama administration tax credit that requires a contract be signed by the end of April, indicating a rebound in sales will soon emerge. Sustained gains in employment would ensure that sales continue to rise even after the government incentive expires, raising the odds the economic recovery is maintained.

“There’s an underlying trend of improvement in housing related to improving affordability and consumer confidence,” said Richard DeKaser, chief economist at Woodley Park Research in Washington.

Economists forecast the gauge would be unchanged after a previously reported 7.6 percent drop for January, according to the median of 33 projections in a Bloomberg News survey. Estimates ranged from a decline of 3.5 percent to an increase of 5.5 percent.

The increase “may signal the early stages of a second surge of home sales,” Lawrence Yun, the group’s chief economist, said in a statement. “We need a second surge to meaningfully draw down inventory and definitively stabilize home values.”

Pending sales are considered a leading indicator because they track contract signings. The Realtors’ existing-home sales report tallies closings, which typically occur a month or two later. The pending sales data go back to January 2001, and the group began publishing the index in March 2005.

Reports last month showed the housing market was faltering. Sales of existing homes fell in February for a third straight month, while purchases of new homes dropped to the lowest on record.