Sony Corp said on Wednesday it has made available over 1 million public domain books on its electronic readers via Google Inc's Books project, which digitizes classic titles not protected by copyright.

Sony, Amazon.com, Barnes & Noble Inc and others are racing to beef up their offerings to meet growing demand for digital books on electronic readers: tablet-like devices where whole books can be stored and read.

Although the devices do not appeal to all readers, due to their cost and technical issues yet to be fully resolved, the companies are trying establish a toehold in a market they believe will eventually become a profit driver.

Sony said the addition of Google's library gives it the largest, most comprehensive array of electronic books available in the market.

Last week, U.S. bookseller Barnes & Noble announced what it touted as the world's largest online bookstore, with more than 700,000 titles. That selection includes more than half a million public domain books from Google.

Amazon's Kindle store offers over 300,000 titles. The Seattle-based online retailer said it would not comment on whether it planned to include Google's titles as well.

Sony was the first to market with its Sony Reader in 2006 and now sells two versions of the device. The launch of the Sony Reader was eclipsed a year later when Amazon entered the market with its Kindle, now also sold in two formats.

Privately owned Plastic Logic plans to enter the market early next year with its own e-reader, and Barnes & Noble said it will be that device's exclusive provider of digital books.

One major issue impeding consumer adoption of digital readers is the closed system used by Amazon and others.

In Amazon's case, titles purchased through the Kindle Store can only be read on the Kindle, while Barnes & Noble's titles are accessible on a range of devices from Apple Inc's iPhone or Research in Motion Ltd's Blackberry, but not on the Kindle or Sony Reader.

(Reporting by Alexandria Sage; Editing by Tim Dobbyn)

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