SACRAMENTO—More homeowners are having trouble making mortgage payments on homes they bought during the Sacramento region’s housing boom, which has cooled over the past several months.

Sacramento County lenders filed 321 notices of default in December _ the highest number in nearly three years. Statewide, 5,582 notices were filed, according to DataQuick Information Systems, which tracks county property records.

While the notices are the first step in the foreclosure process, only about 5 percent of homeowners in default last year lost their homes. Most delinquent homeowners either make payment arrangements with their lender or sell the house and pay off the loan.

It took Dustin Suposs and his girlfriend just eight months to get into financial trouble after getting a no-money-down mortgage on their $365,000 home in Elk Grove, a suburb south of the state capital. Their $2,300-month mortgage payment was triple what they had been paying for rent, and they’ve now fallen two months behind on the mortgage.

“There were a lot of nights of restless sleeping,” Suposs said, before a relative agreed to buy their house.

Until last year, soaring real estate prices meant people could still sell their homes at a profit even if they started falling behind on mortgage payments _ or use equity in their home to convert a risky loan into a conventional one with better terms and lower payments. But prices have leveled off or fallen in many areas, taking away those options.

More homebuyers could be in for a shock over the next two years as their low introductory interest rates expire or their interest-only payments end. Adding to the problem, some borrowers hurt their credit score or took out loans, eating up what little home equity they built up.

“Everyone was anticipating getting in (a house) at any cost and then letting appreciation in the market handle it in the next year or two,” said John Arvanitis, president of Sunrise Vista Mortgage Corp. in Citrus Heights. “In theory, that’s great if appreciation stays at certain levels, but it’s not happening anymore.”