Washington ? The number of buyers who agreed to purchase a home fell sharply in January, a sign that demand for housing is sinking.

As stormy weather slammed Eastern states, an index that tracks sales agreements fell 7.6 percent from December to a seasonally adjusted January reading of 90.4, the National Association of Realtors said Thursday. It was the lowest reading since last April.

The weakness, however, was not confined to the Northeast. The biggest month-to-month drop was in the West, where sales fell 13 percent. Sales fell almost 9 percent in the Northeast and Midwest and 2 percent in the South.

The index is considered a barometer for future sales because typically there is a one- to two-month lag between a signed sales contract and a completed deal. A reading of 100 is equal to the average level of sales activity in 2001, when the index started.