By David Streitfeld, Times Staff Writer

Houses abandoned to foreclosure are beginning to breed trouble, adding neighbors to the growing ranks of victims.

Stagnant swimming pools spawn mosquitoes, which can carry the potentially deadly West Nile virus. Empty rooms lure squatters and vandals. And brown lawns and dead vegetation are creating eyesores in well-tended neighborhoods.

In Northridge, the house next door to Michael McKenna's was put on the market, sold and then foreclosed on, all in the space of a few months last spring.

With the five-bedroom home now forsaken and deserted, McKenna has been reluctantly cutting the lawn and dumping chemicals in the pool to kill the bugs.

"I resent having to do this," the former studio production manager said. "It's breaking my back."

More than 100 houses a day are being foreclosed on in Southern California, up from 13 a day last year. That's still a relative handful for such a populous area, but even the optimists predict that the problem will soon get much worse.

If the foreclosure trend continues on its current pace, experts warn, communities will need to act decisively to avoid blight.

"We know it's coming," said Tina Hess, the assistant Los Angeles city attorney who handles housing enforcement and problem properties.

Hess is proposing that the number of inspectors in L.A.'s vacant-building program be nearly doubled, from the current 15 to 27. Inspectors can order pools to be fenced and houses to be secured against trespassers.

Homeowners like McKenna, 47, and his friend Israel Del Pino, 54, who lives on the other side of the foreclosed property, are eager for stepped-up enforcement. Their efforts to contact an owner, lender or real estate agent responsible for the house have proved fruitless.

"We're getting the raw end of the deal here," McKenna said. "No one will take responsibility."

In another Los Angeles cul-de-sac, this one off Coldwater Canyon Drive near Beverly Hills, the neighbors have the opposite problem. Here's a foreclosed house that should be empty and isn't.

The mansion in question was bought by a man in early 2005 for $1.4 million. By last fall he was gone and the property was in foreclosure.

HSBC, a major lender that was carrying the biggest note on the house, asked Leo Nordine, a real estate agent who specializes in foreclosures, to represent it for sale.

Nordine went to check out the property and realized that people were living there. He left them a polite letter on the kitchen counter. There was no response to that letter, nor to follow-ups that he mailed.

Neighbors, who asked that their names not be used because they were worried about their safety, said the occupants were a group of men apparently in their 20s and 30s. The men take the trash out every week, but that was the only good thing the neighbors had to say.

Nordine said that HSBC was pursuing a formal eviction but that it would probably take many months. The HSBC manager in charge of the foreclosure didn't respond to questions.

On a recent evening, the front door was open. The inhabitants declined to respond to a reporter's queries.