CHICAGO (Reuters) - Wal-Mart Stores Inc. on Saturday said that sales at its U.S. stores grew 6.3 percent to a record $1.52 billion on the day after Thanksgiving, up from $1.43 billion on the same day a year earlier.

Separately, ShopperTrak, which measures retail sales, said retail stores took in $7.2 billion in sales on Friday, up 4.8 percent from a year earlier.

Both increases could indicate that the big retail weekend was living up to expectations for improvement over last year, when the holiday season generated the smallest sales gain in more than 30 years. Wal-Mart is the nation's largest retailer.

But overall, Saturday's sales looked set to slow from Friday's frenetic pace as many stores opened later and some shoppers stayed home after a busy day on Friday. Many big retailers had opened early, at 6:00 a.m. ET, on Friday.

The weather was expected to be dry for most of the country on Saturday, but a band of snow and ice was moving across the U.S. Northeast, and showers hit parts of northern California and the U.S. Northwest.

Mall operators and retailers reported fewer shoppers camping out for early-bird specials on Saturday morning, although parking lots were beginning to fill at some East Coast shopping centers.

"Today it is a little bit slower, no question," said Julie Goldman, general manager of The Falls shopping center in Miami.

She said the parking lot around Macy's department store, which opened at 7:00 a.m., was about 97 percent full by 10:00 a.m.. Other parts of the shopping center -- where stores opened later -- were still relatively quiet.

"It's a little quieter than yesterday at the same time," said Mike McAvinue, general manager of The Mall at Short Hills in New Jersey. "We had a great Friday."

McAvinue said the parking lots were about 80 percent full as of 11:00 a.m. on Saturday, and high-end boutiques such as Tiffany & Co. reported strong demand.

In Dublin, Ohio, The Mall at Tuttle Crossing reported better sales than a year ago, but Saturday's crowds were smaller than Friday's.

"There were certainly no lines to get in," said marketing director Chad Doritan. "Things are okay this morning but yesterday was absolutely a zoo. Most of our stores said they felt that traffic and sales were up from last year."

Last year, many retailers reported very strong after-Thanksgiving sales, but demand tapered off after that.

Black Friday" gets its name from the hope that on that day merchants' financial statements will move out of the red and into the black. The traditional start to the holiday shopping season generates as much as 40 percent of annual revenues and nearly all the year's profits for key gift destinations such as toy stores and apparel chains.

Black Friday was once the biggest shopping day of the year, but in recent years that title has gone to the Saturday before Christmas. This year is likely to be no exception.

The National Retail Federation (NRF), the industry's largest trade group, expects industry sales for the key November and December shopping period to grow 5.7 percent, the largest rise since 1999, to $217.4 billion.

But despite the NRF's bullish outlook, some industry watchers are cautious.

The consensus among analysts is that holiday spending this year will be solid, if not spectacular, averaging a smaller 4 percent growth.

"The consumer is jittery," said Richard Hastings, chief retail analyst with Bernard Sands. "Rising debt levels, inflation and higher gasoline prices are all real threats and a drag on spending."

Despite signs of a pickup in the economy and an improving labor market, consumers don't appear to be feeling the Yuletide cheer.

"The economy still has to prove itself and create millions of new jobs," Hastings said.

The Conference Board in a survey last week said U.S. households on average are expected to spend $455 on gifts this year, down 5 percent from 2002.