Google, stepping up competition with Amazon.com, will open an online store for electronic versions of books in the U.S. this month and internationally in 2011, according to a person familiar with the company’s plans.

The Mountain View, Calif.-based company is working with book publishers to sell hundreds of thousands of e-books, said the person, who asked not to be identified because details of the project haven’t been made public.

Google aims to use its position as the world’s most popular search engine to erode Amazon’s dominance of e-books, while Apple Inc. harnesses the iPad tablet and iTunes online store to make its own inroads. The competition means Amazon’s share of digital books will decline to 35 percent over the next five years from 90 percent in early 2010, New York-based Credit Suisse Group estimated in February.

With Google’s effort, each publisher is negotiating different revenue-sharing arrangements, though all of them will keep the majority of the money from each sale, the person said.

Michael Kirkland, a spokesman for Google, confirmed the company’s plan to start an online bookstore this year but declined further comment.

Google Books, a separate initiative to scan books and offer publishers ways to sell them online, has been held up in court until a settlement with publishers is approved.