Google Inc. is giving $3 million to the U.S. Library of Congress to help set up a system for creating digital copies of rare documents from around the world — the latest step in Google's crusade to expand the amount of information that can be indexed by its Internet-leading search engine.

With the donation announced Tuesday, Google becomes the first business to back the "World Digital Library," a concept that began to take shape about five months ago.

The worldwide program is loosely modeled after the Library of Congress' American Memory project launched 11 years ago.

Backed with $48 million in private donations and a $15 million infusion from the federal government, the American Memory site now has more than 10 million items, including early maps of the United States as well as photos and letters from the Civil War.

Librarian of Congress James Billington now wants to create similar sites devoted to other cultures outside the United States and Europe.

Although nothing has been finalized, Billington initially envisions devoting large sections of the World Digital Library to material from China, India and Islam.

"Much of this will be one-of-a-kind material that you won't be able to find anywhere else," Billington said during a Monday interview. "Getting the material out there [online] is really important. We have already preserved a lot of material that might have perished in other hands."

Google co-founder Sergey Brin characterized the donation as no-brainer for his Mountain View, Calif.-based company as it pursues its avowed mission "to organize the world's information and make it universally accessible and useful."

"This is a philanthropic initiative for us," Brin said during a Monday interview. "It's all about making more information available to more people."

Google's motives aren't entirely altruistic. Because Google makes most of money from the ads that appear when Web surfers are searching for something, the company stands to profit whenever more material comes online.

With an estimated 45 percent share of the U.S. search market, Google earned $1.1 billion on revenue of $4.2 billion during the first nine months of the year. The donation represents a pittance for Google, which had $5.5 billion in cash through September.

It's unlikely all the documents included in the World Digital Library will be indexed by Google or other search engines. That's because the technology that search engines use to crawl the Web still can't figure out how to recognize some documents, like handwritten letters. But Brin expects Google to eventually figure out a way to index almost everything in the World Digital Library.

As part of its quest to bring more information online, Google last year set to scan millions of books in five major libraries.

That project is now being challenged in court by several major publishers and a group of authors suing to thwart Google's plans to make digital copies of copyrighted material without prior permission.

The World Digital Library plans to focus on material no longer protected by copyright. Relatively few books are involved in the Library of Congress project, Brin said. "This will really take us farther out on the frontier," he said.