Wal-Mart Stores Inc., working to reverse six straight quarters of stagnant U.S. sales, will cut prices on more than 20,000 items to get a jump on competitors before the holiday season.

To improve customer service, the world’s largest retailer plans to open more checkout lines during peak shopping times, executives said on a conference call. Wal-Mart is also considering matching in-store prices with online competitors if a customer asks, they said.

Wal-Mart is entering a crucial holiday season under Chief Executive Officer Doug McMillon, who took the helm in February. The chain cut its full-year sales forecast this month as McMillon acknowledged it needed to do a better job stocking shelves and staffing stores, two staples of retail.

The discounting will last 90 days and begin with price cuts focused on electronics and toys. A 48-inch Samsung television will be reduced more than 20 percent to $348. Mattel Inc.’s Barbie Dreamhouse will sell for $120, down from $149. Wal-Mart provided the same kinds of promotions, which the company calls “rollbacks,” last year after Halloween.

Wal-Mart will also reduce online prices on Nov. 2 for a 24- hour period, featuring what it described as 15 deals that are comparable to the ones found on Black Friday. These include a Crayola Paint Maker for $12, reduced from $19.

The company is testing a plan to match online competitors’ prices at stores in Atlanta; Charlotte, North Carolina; Dallas; Phoenix; and northwest Arkansas. Individual store managers are already allowed to match online prices if they want, the company said.

Shares of the Bentonville, Arkansas-based company rose 0.1 percent to $76.45 at the close in New York. They have dropped 2.8 percent this year.