SEATTLE  Amazon.com will introduce two new versions of the Kindle e-reader on Thursday, one for $139, the lowest price yet for the device.

Amazon is hoping to convince even casual readers that they need a digital reading device. By firing another shot in an e-reader price war leading up to the year-end holiday shopping season, the e-commerce giant turned consumer electronics manufacturer is also signaling it intends to do battle with Apple and its iPad as well as the other makers of e-readers like Sony and Barnes & Noble.

Unlike previous Kindles, the $139 “Kindle Wi-Fi” will connect to the Internet using only Wi-Fi instead of a cellphone network as other Kindles do. Amazon is also introducing a model to replace the Kindle 2, which it will sell for the same price as that model, $189. Both new Kindles are smaller and lighter, with higher contrast screens and crisper text.

“The hardware business for us has been so successful that we’re going to continue,” Jeffrey P. Bezos, Amazon’s chief executive, said in an interview at the company’s headquarters. “I predict there will be a 10th-generation and a 20th-generation Kindle. We’re well-situated to be experts in purpose-built reading devices.”