New York ? First it was books. Now it’s DVDs.

Wal-Mart Stores Inc. started another price war Thursday, trimming the online preorder prices of some upcoming DVDs following its price cut on books last month. And, once again, competitors Amazon.com and Target scrambled to match the prices.

It’s the latest salvo in an ongoing online push by Wal-Mart designed to make sure everyone knows it intends to be the low-price leader on the Web, as well as in stores.

The retailer, based in Bentonville, Ark., said late Thursday that it would lower the online prices of new DVDs such as “Harry Potter and the Half Blood Prince” and “Star Trek XI” to $10.

But when Amazon reduced some of its DVD prices to $9.99, Wal-Mart shot back by cutting its DVDs to $9.98 as of Friday morning. Target got into the act Friday morning, too.

All three companies also sweetened the pot by offering free shipping for the DVDs being sold.

The goal of such tactics is to drive higher volume, said BMO Capital Markets analyst Wayne Hood. He noted that some businesses like Wal-Mart and Target can afford to lower their prices and still be profitable because of their low-cost distribution models.

But not all retailers appear to be engaging in the tug of war, as Best Buy Co., Barnes & Noble Inc. and Borders Group Inc. all had higher prices for some of the DVDs on Friday.

Wal-Mart generated more than $400 billion in sales last year.