NEW YORK (CNN/Money) - U.S. consumer confidence tumbled in December amid a continuing weak job market and a tepid holiday shopping season, a research group reported Tuesday.

The Consumer Confidence Index dropped to 80.3 in December from a revised 84.9 in November, according to the Conference Board, a private business research group. The index has fallen for six of the past seven months, and December was much weaker than economists' forecasts of 86, according to Briefing.com.

"The major factor dampening consumers' spirits has been the rising unemployment rate and the discouraging job outlook," said Lynn Franco, director of the Conference Board's Consumer Research Center, adding that until there is an improvement in labor market conditions, there is little likelihood of an upturn in confidence.

Consumer confidence is closely watched by economists and businesses for clues about spending, which makes up two-thirds of the U.S. economy. Holiday sales were lackluster in the days leading up to Christmas as consumers reined in spending, with the unemployment rate jumping to an eight-year high and talk of war dominating the news.

"This was not good news for the economy. It looks like a reflection of November's unemployment rate, which was not high by historical standards, but was moving in the wrong direction," said Gregory Miller, chief economist with SunTrust Banks. "Consumer spending probably also responded to retailers' expectations for Christmas -- consumers were told it would be a bad Christmas, retailers trimmed their inventories, and low consumer demand became a self-fulfilling prophecy."

The Present Situation Index, a measure of consumers' current attitudes about the economy and their finances, plunged to 69.9 in December from a revised 78.3 in November. The Expectations Index, a gauge of consumers' six-month outlook, slipped to 87.2 from 89.3. And consumers reporting "jobs hard to get" rose to 29.8 percent from 27.3 percent.

"It was surprisingly weak in confidence," noted Astrid Adolfson, economist with MCM Moneywatch. "People are viewing the job market as very weak... that accounts for most of the confidence weakness. So we're not ending on a good note."