NEW YORK (CNNMoney.com) -- Retail sales fell for the sixth straight month in December, the longest consecutive stretch of monthly declines in the measure in at least four decades.

The Commerce Department said Wednesday that retail sales tumbled 2.7% last month, compared with a revised 2.1% drop in November.

Economists surveyed by Briefing.com on average had forecast a decrease of 1.2% for December.

Sales excluding autos and auto parts also fell a much worse than expected 3.1% in December compared to a revised 2.5% decline in November.

Economists had forecasted a decrease of 1.3% in the measure, according to Briefing.com

"We've never had this long stretch of declines," said Michael Niemira, chief economist with the International Council of Shopping Centers (ICSC), who has analyzed the government's monthly retail sales numbers going as far back as 1967.

"This current situation is a reflection of a tough, tough environment," he said. "Consumers are buying only essential items. Credit restraints have really impacted sales of big ticket purchases."

"Moving forward, the question is whether this is the low point and could we get some moderation in retail sales in 2009," he said. "We haven't seen a lot of convincing data to that effect."