An equal number of U.S. shoppers sought to buy items online as they did in physical stores over the Thanksgiving weekend, according to a closely watched survey by the leading retail industry lobby, highlighting the growing importance of e-commerce during the crucial holiday shopping season.

In releasing its survey on Sunday, the National Retail Federation also said it was sticking by its forecast for retail sales growth of 3.7 percent in November and December, a slight deceleration from 4.1 percent growth over the holidays last year.

The NRF said that its survey of 4,281 consumers showed that shoppers on average spent or planned to spend about $300 over the weekend, which runs from Thursday, Nov. 26 through Sunday, Nov. 29. That is down from about $381 over the same weekend last year, although the NRF said those numbers are not comparable because it changed the survey's methodology.

The change in methodology came after the survey fell under scrutiny in recent years, including last year when it showed average spending had dropped 6.4 percent and total spending over the weekend slid 11 percent to $50.9 billion. The NRF dropped the total spending projection from this year's survey.

NRF President and Chief Executive Officer Matthew Shay said the outlook for the holiday season remained solid, given the low unemployment rate, lower gasoline prices and other factors.

"Consumers are in a good place to get us to a very good holiday season," Shay said on a call with media.

The survey projected that more than 151 million people shopped either in stores and/or online over the weekend, up from the 136 million projection in an earlier mid-November survey.

The survey estimated that more than 103 million shopped online over the weekend, compared with nearly 102 million in stores.