Google has expanded its controversial book search service to allow people to download whole copies of books in PDF format to their computers, with the ability to print them out.

The feature will go live Wednesday at the service's Web site (http://books.google.com), said Adam Smith, group product manager of Google Book Search and Google Scholar.

The books available for download will only be those that are in the public domain and thus not protected by copyright, Smith said. Until now, people have been able to read these public-domain books on the Google Book Search Web site, but not download and print them, he said.

Google will not allow downloading of copyrighted books, not even those for which it has obtained permission from the copyright holders to display their full text, Smith said.

The vast majority of the public-domain books available for download have been scanned as part of the library project of the Google Book Search service, Smith said. For the project, Google is scanning portions of the collections of some of the world's largest academic libraries, including Google partners Harvard University, Stanford University and Oxford University.

However, critics say Google can't scan copyrighted books it obtains from the libraries unless it gets permission from the copyright holders. The issue is at the center of two separate lawsuits brought against Google last year, one by The Authors Guild and three authors, and another one by The Association of American Publishers on behalf of five of its members: The McGraw-Hill Companies, Pearson Education, Penguin Group USA, Simon & Schuster and John Wiley & Sons.