SAN DIEGO — Increases in Southern California home prices cooled in September as the supply of properties for sale grew and investor purchases waned, a research firm said Wednesday.

The median sales price for new and existing houses and condominiums in the six-county region was $382,000, up 21.3 percent from $315,000 the same period last year, DataQuick said. It was the 14th straight month of double-digit annual percentage increases but the median fell from the previous month for the first time since February, dropping by $3,000 from new five-year highs set in June, July and August.

There were 19,112 homes sold, a 7 percent increase from 17,859 homes in September 2012.

The more modest price increases, coupled with higher sales, are the latest sign that the market is taking a breather. As prices soared during the first half of the year, more sellers came off the sidelines, easing tight supplies.

Some of the median price increase reflects a shift in sales to more expensive homes. Sales below $300,000 tumbled 25.3 percent from last year, while sales between $300,000 and $800,000 surged 25.5 percent and sales above $800,000 skyrocketed 43.4 percent.

Sales of less expensive homes were limited by inadequate supply, DataQuick said. Many owners couldn't afford to sell because they owe more than their properties are worth and lenders are shying away from foreclosures.

Properties that were foreclosed upon during the previous year accounted for only 6.3 percent of existing home sales, down from 16.6 percent a year earlier and 56.7 percent in February 2009.

Absentee buyers, who are mostly investors, accounted for 26.3 percent of all sales last month, down from 27.7 percent a year earlier and the lowest level since November 2011. Absentee buyers peaked at 32.4 percent of sales in January, well above the monthly average of 18.4 percent since the San Diego-based research firm began keeping track in 2000.

Buyers paying all cash accounted for 27.6 percent of September sales, down from 32.2 percent a year earlier and the lowest since September 2010. The percentage of cash buyers has slipped every month since hitting 36.9 percent in February.