WASHINGTON — Sales of new single-family homes rose almost 18 percent in December to the highest rate since last spring, but builders in 2010 still suffered through their worst year since record-keeping begin in 1963.

Sales jumped to an annual rate of 329,000 on a seasonally adjusted basis, with almost three-quarters taking place in the West, according to the Commerce Department. Economists polled by MarketWatch had predicted sales would rise to an annual rate of 299,000.

The market might have gotten a jolt from a tax credit in California that expired at year’s end, some economists say.

“The impressive increase in new home sales in December is mainly due to the rush to beat the deadline of a tax credit in California,” the firm Capital Economics said in a report. “Without that boost, new sales would have been broadly unchanged.”

Whatever the case, new home sales in 2010 ended up at the lowest level on record. The government estimates that sales fell 14 percent last year to 321,000 from 375,000 in 2009.

Sales plunged during the recent recession, and with millions of homeowners threatened with foreclosure, the housing market continues to struggle to recover.

Economists expect sales to accelerate in 2011 as the U.S. economy improves and buyers are attracted by low prices and ultra-low interest rates. Yet the rate of growth will depend largely on how fast the 9.4 percent unemployment rate sinks.

The lack of work has hurt many homeowners, and the fear of losing a job has scared off prospective buyers, creating a surplus of available homes. Builders have reacted by slowing new construction.

And at the end of 2010, about 190,000 homes were available for sale, the fewest on the market since 1968, according to the Commerce Department.

The median price of new homes, meanwhile, climbed to $241,500 in December from $215,500 in November.