Sales of existing single-family homes fell 2.2 percent in September after an unexpectedly strong sales spurt earlier this year, a real estate trade group reports.

The National Association of Realtors said sales of existing homes declined to a seasonally adjusted annual rate of 3.63 million units last month, following a 2.2 percent increase in August and a 5.0 percent decline in July.Sales had increased every month from February through June, suprising economists who had predicted that gradually rising interest rates would dampen home buying. However, as it turned out, many buyers apparently bought early in an attempt to beat rising rates.

"The decline ... in September is a hangover from the buying spree of the summer," said John A. Tuccillo, chief economist of the real estate group. "The extraordinary increase" of the summer was "in part borrowed from September."

Fixed-rate mortgages hit a low of 9.84 percent in February and rose to 10.71 percent by early August. Since then, they've eased back to 10.28 percent.

Tuccillo predicted sales rates will continue to lag in the fourth quarter and by year-end would total 3.47 million units, down only slightly from 3.53 million in 1987.

The median price of a home fell from August to September by $2,900 to $88,500, meaning half sold for more and half for less. The decline was a normal seasonal development as the summer home-selling season drew to a close, Tuccillo said.

The Northeast remained the costliest region of the country, with a median sales price of $141,400, up 6.3 percent from a year ago. In the West, the median price was $124,300, up 7.1 percent from a year earlier. The median in the South was $82,400, up 3.6 percent from September 1987.

The West was the only region of the country showing an increase of sales last month. They rose 6.0 percent to 710,000 units, following a 3.1 percent increase in August.

Sales fell 5.8 percent in the Northeast to 650,000 units, the lowest level since January. They fell 3.2 percent in the Midwest to 900,000 units and were off 2.8 percent in the South to 1.38 million units.