Foreclosures in Los Angeles County rose for the first time in 31 months in July, according to a report released Thursday.

One in every 3,202 homes was in foreclosure in the county, up more than 10 percent from the same month last year, according to RealtyTrac, an Irvine real estate data firm. On a month-to-month basis, the rate rose nearly 6 percent from June.

In the six-county Southern California region, there were 7,908 foreclosures, up about 6 percent from the same month last year, and up 4 percent from June.

Amid a tight supply of available homes for sale, there is some evidence that banks are moving more aggressively to clear problem mortgages off their books by moving ahead with foreclosures, according to some housing experts.

Daren Blomquist, vice president at RealtyTrac, said that while foreclosure activity fell nationwide for the 46th straight month, that wasn’t the case in all markets.

“The number of state and local markets with persistent foreclosure problems is becoming fewer and farther between, although there were some surprise spikes in foreclosure activity in July in markets that had previously been experiencing long-term downward trends in foreclosure activity,” he said.

In the greater Valley, Palmdale again topped the list, with foreclosures in one out of every 392 homes. The other major Antelope Valley city of Lancaster also continued to struggle, with one out of every 454 homes in foreclosure.

Other Valley communities with high foreclosure rates include Sunland, with one in every 464 homes; Pacoima, with one in every 582; and Sylmar with one in every 638.

Among Valley communities with few foreclosures were La Canada-Flintridge, with one in every 3,626 homes; Glendale, with one in every 1,773; Studio City, with one in every 1,533.