WASHINGTON — US homebuyers pulled back in July, as sales declined amid a shortage of available properties and steadily rising prices. Sales of existing homes fell 3.2 percent last month to a seasonally adjusted annual rate of 5.39 million, the National Association of Realtors said Wednesday. The decline marks a reversal from rising demand that pushed sales in June to their highest level since February 2007. Fewer homes are coming onto the market, putting a cap on the sales growth enjoyed earlier this year thanks in part to a low mortgage rate and brightening job market.