For years, Wal-Mart has used its clout as the nation’s largest retailer to squeeze competitors with rock-bottom prices in its stores. Now it is trying to throw a holiday knockout punch online.

Starting Thursday, Wal-Mart Stores plans to offer free shipping on its Web site, with no minimum purchase, on almost 60,000 gift items, including many toys and electronics. The offer will run through Dec. 20, when Wal-Mart said it might consider other free-shipping deals.

“Everyone’s trying to figure out how we can serve a customer that’s trying to save every penny they can,” said Steve Nave, senior vice president and general manager of Walmart.com. “It’s the most competitive offer out there, and we’re pretty excited about it.”

Even before Wal-Mart’s surprise move, shipping prices were this holiday season’s predicament for online retailers. In a bid for cost-conscious consumers, Target and J. C. Penney introduced their most aggressive free-shipping programs ever, and Sears, Toys “R” Us, Williams-Sonoma and others were trying to match the success of Amazon’s shipping program, offering unlimited two-day shipping for an annual fee.