An index that forecasts near-term home sales fell in August to a record low as would-be home buyers had difficulty getting mortgages.

The National Association of Realtors said Tuesday its seasonally adjusted index of pending sales for existing homes fell 6.5 percent from July and 21.5 percent from a year ago.

August's reading of 85.5 was below analysts' expectations and the lowest ever for the index, which started in January 2001. Analysts surveyed by Briefing.com had predicted the index would fall by 2 percent from July.

The pending home sales index is designed to predict sales levels over the following two months. A reading of 100 is equal to the average level of pending sales activity in 2001, when the index began.