Holiday sales rose 3 percent, a major retail trade organization said Tuesday, well below its forecast for a 4.1 percent gain.

The figures offer the latest evidence that shoppers held back on spending amid economic uncertainty in a season that accounts for as much as 40 percent of stores' annual revenue.

The National Retail Federation, the nation's largest retail industry group, said retail sales for November and December combined totaled $579.8 billion. December sales rose 2.1 percent, while November sales rose 3.9 percent, according to the federation's analysis of government data. The figures are being compared with the year-ago periods.

On Long Island, the picture was more glum than the national scenario. December sales tax collections for Nassau and Suffolk counties fell by 1.9 percent compared to the same month last year. For November and December combined, the region's sales tax collections, which include taxes on a wide range of purchases from clothing to gas and utilities, dropped 0.14 percent. The retail trade industry typically generates about 54 percent of the region's sales tax collections, according to an annual state report released in August 2012.

Many LI independent retailers selling traditional holiday gift items said their holiday sales fell below last year's figures, hurt by household budgets diminished by superstorm expenses, spirits dimmed by the Newtown shooting and "fiscal cliff" worries.

Nationally, the 2012 holiday figures marked the slowest sales growth since 2009, when sales rose 0.3 percent. Holiday sales rose 5.6 percent in 2011 and 5.5 percent in 2010, according to the retail federation.

For the first time, the federation counted online sales and sales from the auto parts and accessories business. But even nonstore sales, which includes online sales, were below expectations for the two-month period. They rose 11 percent, below the 12 percent that the industry projected.

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"For over six months we've been saying that the fiscal cliff and economic uncertainty could impact holiday sales," Matthew Shay, NRF president, said in a statement. "As the numbers show, these issues had a visible impact on consumer spending this holiday season."

The numbers were released as thousands of retail executives are gathering in New York this week for the annual federation's convention to share strategies for 2013 and offer insights into shoppers' mindset.

Retailers are being forced to reinvent themselves as shoppers increasingly shift to the Web and use their mobile devices to shop or do research. According to the federation, non-store sales accounted for 16 percent of holiday sales, up from 15 percent a year ago.

With Keiko Morris