This fall, patrons at the Carnegie Library's main branch will be able to borrow books in a new format -- on a 3-inch-tall MP3 player.

Patrons who own MP3 players (such as iPods) that are compatible with the new service will be able to download a book to their own devices. But patrons without MP3 players won't be left out; instead, they'll just borrow the "book" on a library-owned player.

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In addition, the Carnegie Library has ordered some books on MP3 CDs, which have much more memory than standard CDs. The MP3 CDs can hold an entire book on one or two CDs, compared to 10 or more CDs in the traditional format.

The MP3 CDs are smaller in size than traditional CDs but can be used on most later model CD players.

Both the books on MP3 and the MP3 CDs will be available at the renovated main branch building in Oakland beginning on Oct. 3. The library will initially have six to 10 MP3 players to loan out, said Dallas DiLeo, Carnegie's manager of main library services.

DiLeo added that she expects that many of the initial users of both types of digital audio books will "probably be people who already are audio listeners, although we hope to introduce a lot of new people to audio. We also hope that teens will use it."

Carnegie is one of an estimated 100 library systems around the country that are testing the new technology, said Clara Bohrer, president of the Public Library Association and director of the West Bloomfield Library in Michigan.

"Right now, this whole books on MP3 is in its infancy stage in public libraries," said Bohrer, whose library is about to begin its own test with the MP3 technology. "Libraries that are offering the service for the most part actually have to have the hardware as well."

To ensure that patrons return the MP3 devices, some libraries require them to provide a credit card number, Bohrer said. That's the case with the Kalamazoo, Mich., library, which was the first system in the country to try out the MP3 technology.

But DiLeo said she's reluctant to require patrons to give a credit card number because that would exclude most teens. Instead, she said, any patron who doesn't return the player would be assessed a $110 library fine -- the cost to replace the device.

DiLeo said the Carnegie Library has contracted with Audible.com, a New Jersey-based digital audio book company that offers more than 7,000 books from major publishers. As part of the contract, which DiLeo said is less than $400,000, Audible will provide the library with MP3 devices to lend to patrons.

"We'll get a lot of bang for the buck on this," DiLeo said. "To buy a best seller in cassette format costs over $100. Audible gives us a way to buy it at lower cost."

If a patron wants a particular book and it is available from Audible, DiLeo said, the library would then either download it to the patron's MP3 player or download it onto one of the library's MP3 players and have the patron check it out on his library card.

Patrons could also choose to listen to the book on MP3 CDs, DiLeo said, adding that the Shaler Library also offers books on MP3 CDs. Unlike the digital audio books downloaded directly onto an MP3 player, the MP3 CDs are "a tangible thing" that can be checked out and taken home by patrons, DiLeo said.

Bohrer said she thinks that the necessity of loaning the hardware -- the MP3 player -- is just an interim step for libraries. Eventually, she expects that "libraries will get out of the hardware business" as more patrons have MP3 players.

"It's just like when video recorders were new, and many libraries allowed users to check out VCRs along with videos," Bohrer said.

Whether MP3 CDs or digital content downloaded to MP3 players will be more popular remains to be seen, she added. "It depends on how it progresses," Bohrer said. "We [in the library field] change and evolve in response to shifts in technology and our customers' needs and wants."