A price war is brewing in the growing market for electronic reading devices.

Barnes & Noble, the national bookseller, announced Monday that it was dropping the price of its six-month-old Nook e-reader to $199 from $259 and introducing a new version of the device, which connects to the Internet only over Wi-Fi networks, for $149.

Responding rapidly, Amazon.com then cut the price of its popular Kindle e-reader below the Nook, to $189 from $259.

The price cuts were made as manufacturers of e-readers faced a mounting threat from Apple’s iPad. Even though it is far more expensive than the e-readers, the iPad, which starts at $500, performs a range of functions with a versatile, colorful display that contrasts sharply with the static, monochrome screen of e-book readers. Apple said it sold more than two million iPads in the two months since the tablet’s introduction.

“It was obvious that the price of stand-alone e-readers had to come down,” said James McQuivey, an analyst at Forrester Research, citing the threat by Apple and other tablet makers. “We just never thought it was going to happen this rapidly.”