Retailers have not recouped all of the $1 billion in sales postponed by shoppers as they dug out from last month's East Coast blizzard, research firm ShopperTrak said on Wednesday.

Total U.S. retail sales rose 6.5 percent in the week that ended on Saturday, with foot traffic up 4.1 percent, according to ShopperTrak.

ShopperTrak founder Bill Martin said some of the sales put off by the blizzard, which dumped as much as three feet of snow in parts of the Northeast, could come in January.

There will be some continued momentum this week and into the weekend as consumers continue to dig out, Martin said.

Despite the snow, ShopperTrak said it still expected retail sales to be up 4 percent for the entire holiday period, citing a strong November.

The National Retail Federation has forecast seasonal retail sales will be up 3.3 percent, compared with a 0.4 percent increase last year and a 3.9 percent fall in 2008.

U.S. online sales fared substantially better during the holiday period, rising 12 percent in November and December, according to research firm comScore.

Sales through the Web, which have been growing more rapidly than those at brick-and-mortar stores, reached $32.6 billion during the period, still just a fraction of overall retail sales.

Top U.S. retailers, including discounter Target Corp and department store chain Macy's Inc, are set to report December sales results on Thursday.

Separately, MasterCard Advisors SpendingPulse said clothing sales were up 10.9 percent in December. Consumer electronics fared less well, with sales up only 1.5 percent, largely because of lower price tags on televisions, SpendingPulse Vice President Michael McNamara told Reuters.

(Reporting by Phil Wahba and Alexandria Sage, editing by Dave Zimmerman and Lisa Von Ahn)