As restaurant chains begin rolling out holiday promotions, researchers project a challenging season for sales.

However, some say slightly lower unemployment rates and gas prices may lift budgetary pressures for consumers in higher income brackets — which could give restaurants a slight boost in November and December.

Last week the National Retail Federation, or NRF, projected that retail industry sales for the months of November and December will increase 2.8 percent to $465.6 billion this season, compared with a 5.2-percent increase last year.

While the NRF projection does not include restaurants, the holiday shopping season is a key indicator for the foodservice industry, as it struggles to attract cash-strapped consumers.

“Just when you think the U.S. economy is turning around, another factor comes into play that changes the game,” said NRF chief economist Jack Kleinhenz in a statement. “Persistently high unemployment, an erratic stock market, modest income growth and rising consumer prices are all combining to impact spending this holiday season.”

A retail report by The NPD Group found that most consumers, 64 percent, are planning to spend the same amount on holiday gifts this year, compared with 2010. Only 9 percent said they plan to spend more, according to the Port Washington, N.Y.-based market research firm’s 10th Annual Holiday Retail Outlook report, released last week.

New retail sales figures for September are expected Wednesday, giving analysts more to work with in predicting holiday trends.

Hudson Riehle, senior vice president of the National Restaurant Association’s research and knowledge group, said restaurant industry sales have been running at about a 3-percent increase so far this year, “and there’s no reason to think it will diminish substantially over the fourth quarter.”