New single-family home sales unexpectedly fell in December for the first time in four months and the median home price dropped, dampening some of the hopes the housing sector will boost the economy this year.

The Commerce Department said on Thursday sales decreased 2.2 percent to a seasonally adjusted 307,000-unit annual rate.

Economists polled by Reuters had forecast sales at a 320,000-unit rate. November's sales pace was revised slightly lower.

The housing market remains constrained by high unemployment, falling prices and an oversupply of unsold homes following a bust that triggered the 2007-09 recession.

Sales fell in two of the country's four regions, including a 10.1 percent drop in the South, where most new homes were sold.

The median sales price for a new home fell 2.5 percent to $210,300 last month, the biggest drop in four months. Compared to December last year, the median price was down 12.8 percent.

There were a record low 157,000 new homes on the market last month and at December's sales pace, it would take 6.1 months to clear them, up from 6.0 months in November.

For all of 2011, sales were down 6.2 percent from the prior year, with 302,000 new single-family homes being sold.

(Reporting by Jason Lange; Editing by Andrea Ricci)