WASHINGTON (AP) — Americans retreated from signing contracts to buy homes in April for the second straight month, a possible sign that a declining number of homes on the market are stifling sales during the traditional spring buying season.

The National Association of Realtors says that its pending home sales index fell 1.3 percent in April to 109.8, after slipping 0.9 percent in March to 111.3.

Potential buyers are crowding open houses in many neighborhoods because there are fewer sales listings. The number of properties for sales has plunged 9 percent over the past year to 1.93 million, according to the Realtors

Pending sales contracts are a barometer of future purchases. A sale is typically completed a month or two after a contract is signed.