The number of buyers who agreed to purchase previously occupied homes fell sharply in November, a sign sales will fall this winter, undermining last summer's recovery.

The National Association of Realtors said Tuesday its seasonally adjusted index of sales agreements fell 16 percent from October to a November reading of 96. It was the first decline following nine straight months of gains and the lowest reading since June.

The drop was far larger than the 2 percent expected from economists surveyed by Thomson Reuters, and analysts were surprised.

"This was bound to happen at some point, although not by this much," wrote a startled Jennifer Lee, senior economist with BMO Capital Markets. "Gulp," she added.

The report indicates consumers are taking their time following the extension of a tax credit deadline. The incentive of up to $8,000 for first-time buyers was set to expire at the end of November. But Congress pushed back the date and broadened the program with a new credit of up to $6,500 for buyers who relocate.

"It will be at least early spring before we see notable gains in sales activity as homebuyers respond to the recently extended and expanded tax credit," Lawrence Yun, the Realtors' chief economist, said in a statement.

Typically there is a one- to two-month lag between a contract and a done deal, so the index is a barometer of future sales. Pending sales were down 26 percent from October in the Northeast and Midwest, 15 percent in the South and 3 percent in the West.

The housing market had been rebounding from the worst downturn in decades, aided by aggressive federal intervention to lower mortgage rates and bring more buyers into the market. Home resales surged last month to the highest level in nearly three years.

But concerns remain that the market recovery will stall as the federal programs are phased out.