“They were so overwhelmed with the competition that Amazon presented, they just didn’t know what they could do to be competitive in the digital arena,” said Peter Osnos, the founder and editor at large of PublicAffairs, an independent publisher. “Google’s giving them a real shot at doing that.”

Publishers said they were elated that Amazon would have another serious e-book retailing force to contend with. Only last year, Amazon nearly had the e-book market to itself, leading publishers to worry that they were headed toward an Amazon monopoly.

Since then, a vastly more diversified marketplace has emerged. Last fall, Barnes & Noble introduced an e-reader, the Nook, and more recently, an updated color version, the Nook Color. In April, Apple unveiled the iPad, which the company said in October had sold 7.5 million units.

Perhaps most important, five of the six largest publishers of trade books switched this year from a traditional wholesale model to what is known in the publishing industry as an agency model. Under that model publishers set their own prices for e-books, and a retailer acts as an agent of the publishers, taking a 30 percent cut of each sale and leaving 70 percent for the publisher.

A crop of e-readers introduced this year has given consumers more choices, at prices that are competitive, even less than $100. Google e-books will be readable on any open-format e-readers, including the Nook, a development that publishers said would give consumers greater freedom.

“Consumers have been in a position where they had to claim some kind of loyalty,” said Maja Thomas, the senior vice president for Hachette Digital, part of the Hachette Book Group, which publishes authors including Stacy Schiff and James Patterson. “Now they can buy books from their local bookstores online, or from Powell’s, or from Google.”