U.S. libraries are struggling to get up to speed with the new way of reading books -- in digital format on e-readers, librarians and others say.

The Washington Post reported Saturday that in Maryland, for example, the state's libraries doubled their total of copyright e-books available to fewer than 10,000 titles in the past two years, while the number of e-book checkouts statewide nearly quadrupled to 266,000.

The District of Columbia library system witnessed the number of people using their Kindles, Nooks and iPads to download books grow 116 percent from 2010 to 2011, the newspaper said.

The problem is two-fold: libraries' budgets are pinched and some book publishers such as Simon & Schuster, fearing loss of revenue to pirating, refuse to make digital titles available to libraries, the Post said.

"Everything you need and want is there," Paula Isett, outreach specialist with the Maryland Department of Education, who consults with the state's libraries, told the newspaper. "There are unlimited books, and if a library doesn't have a book, they can get it. Our e-book library is not like that. There is such demand, and we're struggling to keep up with it."

Ginnie Cooper, chief librarian of the District of Columbia library system, said her branch managers predict the digital demand is only going to grow exponentially in the next five years from the current 2 percent of total circulation.

"The lowest prediction was 15 percent, and some said they thought it would be half of what we do," Cooper said.

Publishers say despite their centuries-long support of public libraries, they have to be careful given the ability of hacker to grab e-books without paying for them.

Penguin said in November that while it has "always placed a high value on the role that libraries can play in connecting our authors with our readers due to new concerns about the security of our digital editions, we find it necessary to delay the availability of our new titles in the digital format while we resolve these concerns with our business partners."

Albert Greco, a professor at the Fordham University business school who specializes in publishing, says the financial concerns are based in reality.

"U.S. government departments and agencies have been hacked," he said. "If they can be hacked, think about the local public library in Alexandria, Virginia. The odds are its firewall is not as good as the Defense Department's."