The University of California (UC) is joining Google Inc.’s book-scanning project, throwing the weight of another 100 academic libraries behind an ambitious venture that is under legal attack for alleged copyright infringement.

The deal covers all the libraries in UC’s 10-campus system, marking the biggest expansion of Google’s effort to convert millions of library books into digital form since a group of authors and publishers sued last fall to derail the project.

“We think this is a pretty significant step forward,” said Adam Smith, the group product manager overseeing Google’s book-scanning initiative.

UC joins three other major U.S. universities–Stanford, Michigan, and Harvard–that are contributing their vast library collections to Google’s crusade to ensure reams of written knowledge makes the transition to the digital age. The New York Public Library and Oxford University also are allowing portions of their libraries to be scanned.

The project is expected to last years and cost tens of millions of dollars–a bill that Google is footing. It’s something Google can easily afford, given the 8-year-old company has amassed nearly $10 billion in cash.

Google’s motives aren’t entirely altruistic. The Mountain View, Calif.-based company wants to stock its search engine with unique material to give people more reasons to visit its web site, the hub of an advertising network that generates most of its profits.

The endeavor has riled authors and publishers because the participating schools are allowing Google to create digital copies of books still protected by copyright.

Only so-called “public domain” books no longer protected by copyrights will be shown in their entirety. Google doesn’t plan to show anything more than a few snippets from copyrighted material–a “fair-use” approach that the company believes is allowed under U.S. law.

Both the Association of American Publishers and Authors Guild, the two trade groups suing Google, contend the company shouldn’t be allowed to stockpile digital versions of copyrighted material without permission.

Though the lawsuits don’t target the university libraries, UC’s alliance with Google has irritated the publishing community.

“It’s a curious decision to make, given the pending litigation and legal uncertainties” surrounding the project, said Allen Adler, vice president of legal and government relations for the Association of American Publishers.

The lawsuits are expected to remain in the evidence-gathering stage through the remainder of this year.

Google’s arguments in the dispute got a boost in Germany this summer after a publisher there abandoned its effort to prevent its copyrighted works from being copied.

UC’s libraries already have been involved in another book-scanning initiative, called the Open Content Alliance, that is spearheaded by Yahoo Inc. and Microsoft Corp., two of Google’s biggest rivals. That project, which continues, focuses exclusively on books without copyright protection.

The decision to link up with Google to widen the scope of UC’s book scanning was made by university president Robert Dynes without a vote by the board of regents. “There are so many benefits to this,” said Jennifer Colvin, a spokeswoman for UC’s library. “We respect copyrights, but we also want to give full access to our public-domain material.”

In a separate development, Google has begun letting users download and print, free of charge, classic novels and many other, more obscure books that are in the public domain. Using Google’s Book Search service, web surfers hunting titles like Dante’s Inferno and Aesop’s Fables will be able to download PDF files of the books for later reading, to run keyword searches, or to print them on paper. Up to now, the service only allowed people to read the out-of-copyright books online.

Google supports the service by showing its small, keyword-generated text ads on search-results pages. The initiative does not include any books under copyright.