WASHINGTON – Sales of new homes plunged to a record low in January, underscoring the formidable challenges facing the housing industry as it tries to recover from the worst slump in decades.

The Commerce Department reported Wednesday that new home sales dropped 11.2 percent last month to a seasonally adjusted annual sales pace of 309,000 units, the lowest level on records going back nearly half a century. The big drop was a surprise to economists, who were expecting a 5 percent increase over December’s pace.

Although winter storms were partly to blame, home sales have fallen for three straight months despite sweeping government support. Economists were already worried that an improvement in sales in the second half of last year could falter as various government support programs are withdrawn.

”There is no doubt that January and February are going to be messy months for housing, given the severe weather conditions, but that doesn’t take away from the fact that the housing sector has taken another big step back, even with the government aid,” Jennifer Lee, a senior economist at BMO Capital Markets, said in a research note.

A rebound in housing in the second half of last year helped to boost overall economic growth back into positive territory. Each new home built, for example, creates about three jobs for a year and generates about $90,000 in taxes paid to local and federal authorities, according to the National Association of Home Builders.

However, economists are worried that if housing falters in coming months, it will be one more headwind that the recovery will have to overcome. The decline to an annual purchase rate of 309,000 in January was 6 percent below the previous record low set in January last year.

January’s weakness was evident in all regions except the Midwest, where sales posted a 2.1 percent increase. Sales were down 35 percent in the Northeast, 12 percent in the West and almost 10 percent in the South.

The drop in sales pushed the median sales price down to $203,500. That was down 5.6 percent from December’s median sales price of $215,600, and off 2.4 percent from year-ago prices.