WASHINGTON — Pending sales of previously owned homes fell a surprising 6.5% in August as buyers struggled to get loans, indicating the dire housing market could worsen, according to an industry report released Tuesday.

The National Assn. of Realtors pending home sales index fell to a reading of 85.5, the lowest since records began in January 2001.

The previous low for the index of a month’s signed contracts was 89.8 in September 2001 after the terrorist attacks on New York and the Pentagon.

The decline in the home sales index was sharper than the 2.1% drop economists had expected for August and came after sales of existing homes for the month dipped to their lowest level in five years.

“The July number was revised up a bit, to a decline of 10.7%, but this is still absolutely awful, confirming that the existing-homes market is now in free-fall,” said Ian Shepherdson, chief economist at High Frequency Economics. “There is no sign that the bottom of the market is near. With price declines accelerating, real mortgage rates are very high; the downside from here is still substantial.”

Notably, more than 10% of sales contracts fell through late in the process largely due to borrowers’ difficulty in securing credit, according to a Realtors association survey.

“The impact was greater in high-cost markets that are more dependent on jumbo mortgages. In some areas, as much as 30% of signed contracts were falling through in August when the credit crunch problem peaked,” said Lawrence Yun, senior economist at the Realtors association.

Jumbo loans are those valued above $417,000; they are too big to be purchased by government-sponsored enterprises Fannie Mae and Freddie Mac.

The pending-sales index was 21.5% below the August 2006 level of 108.9.