The number of California homeowners who defaulted on their mortgage payments jumped to its highest level in almost 10 years, exacerbated by slowing home sales and adjustable-mortgage resets.

Homes lost to foreclosures in California shot up to 11,033 in the first quarter, an 81.5 percent climb from 6,078 in the previous quarter, according to DataQuick Information Systems. Foreclosures rocketed 802.1 percent from 1,223 in the first quarter last year but remained below the 1996 peak of 15,418.

Statewide, lenders sent 46,760 notices of default to homeowners in the first quarter. That marked a 23.1 percent jump from the previous quarter and a 148 percent jump from a year ago in the same period. Notices of default mark the first stage in the foreclosure process.

John Karevoll, an analyst for DataQuick, said the numbers have catapulted due to a surge of home loans -- many of which were high-risk subprime loans -- that were made in the summer of 2005. The adjustable-mortgage rate on many of those loans was reset a year and a half later, leaving homeowners scrambling to make their payments.

During boom times, homeowners could sell their property or refinance, Karevoll said. "We had a good long run of strong appreciation and default numbers went down significantly," he said.

Today, prices have flattened, making it difficult for homeowners to unload their property.

The Bay Area has been shielded from some of the pain compared with the rest of California because of its higher home prices and wealthier residents. About 60 percent of the homeowners who receive a notice of default are able to make their payments before they lose their homes, Karevoll said.

Nonetheless, default notices in the Bay Area totaled 6,730 in the first quarter, a 160.3 percent increase over last year. Contra Costa experienced the biggest jump in default notices, totaling 1,969 compared with 605 the previous year, marking a 225.5 percent increase.

In San Francisco, default notices rose 67.4 percent to 216 from 129 the previous year. Marin had the second-fewest default notices -- 118 compared with 76 the previous year.

Mark Zandi, chief economist at Moody's Economy.com, said areas like Contra Costa are more susceptible to housing pressures because of the number of lower-income households that take on subprime loans. The Central Valley as well as parts of Southern California face similar challenges.

Zandi said he expects to see more foreclosures later this year, when a peak number of homeowners hit their maximum first payment reset.

Karevoll said foreclosures start to become a problem when they drag prices down on other homes. But he does not expect that to happen in the Bay Area, where lenders are still able to resell foreclosed homes at their market price.

"It's very unlikely that the Bay Area will see discounting," he said.

Bay Area default notices For homes and condos in the first quarter, year over year County/region 2007 Increase San Francisco 216 67.4% Alameda 1,578 179.8 Contra Costa 1,969 225.5 Santa Clara 1,058 100.8 San Mateo 382 105.4 Marin 118 55.3 Solano 914 210.9 Sonoma 407 159.2 Napa 88 87.2 Bay Area 6,730 160.3