Sales of existing homes rose 2.1 percent in August, continuing a three-month rebound, a real estate trade group said Thursday. It forecast a slowdown in the fourth quarter because of rising mortgage rates.

The National Association of Realtors said the resale of homes totaled a seasonally adjusted annual rate of 3.40 million units, compared with July's revised 3.33 million rate. Sales rose 0.9 percent in June from the 1990 low of 3.30 million units in May."Despite rising rates, the resale market is stable and slightly better than July," said Norman D. Flynn, the Realtors' president. "The strength we see largely is due to people who are buying homes in less populous areas and recreational areas."

However, Realtors chief economist John A. Tuccillo said mortgage rates will rise during most of the fourth quarter, having a negative impact on existing-home sales.

Fixed-rate, 30-year mortgage rates rose from 9.84 percent to 10.24 percent in August, according to the Federal Home Loan Mortgage Corp. They averaged 10.16 percent at the end of last week.

The Realtors also said the national median existing-home price was $97,000 in August, down 1.3 percent from July but up 1.3 percent from a year earlier. The median means half of the homes cost more, half less.

Flynn said a decrease in the national median home price from July to August indicates sellers are bringing down prices in response to rising interest rates.

"This is a typical occurrence," he said.

Sales climbed 6.9 percent to 1.40 million units in the South, where the median price was $86,900. They rose 2.2 percent to 950,000 units in the Midwest. The median price there was $75,000.

But sales fell 1.8 percent in the sluggish Northeast to 550,000 units. The median price in the Northeast was $144,900. They also dropped 3.8 percent to 530,000 units in the West, where the median price was $141,600.