Three advocacy groups have asked Google to commit to protect the privacy of readers in its book search service, which is poised for a major expansion under a pending class-action settlement. The groups, the Electronic Frontier Foundation, the American Civil Liberties Union and the Samuelson Law, Technology and Public Policy Clinic at the University of California, Berkeley, have asked Google to limit the data it collects about users’ reading habits, to commit to protect reader records by handing them over only in response to subpoenas or court orders, and to put into effect measures giving users control of their data.

The groups made the requests in a letter to Eric Schmidt, Google’s chief executive. In an accompanying blog post, the groups are urging people to send e-mail messages to Mr. Schmidt demanding privacy protections.

“We’ve asked that Google only respond to legitimate warrants when the government comes calling, for example, and we’ve asked that they not share your private reading data with third parties without your permission, among other things,” the groups wrote.

On its public policy blog, Google said it shared many of the privacy goals raised by the advocacy groups. But Google also said that its expanded book search service would not be built until an landmark settlement of a copyright class action filed by authors and publishers is approved by a court. (That settlement, which will allow Google to build an expansive digital library, has attracted criticism and is currently being scrutinized by the Justice Department for possible antitrust problems.) Because the service has yet to be built, it was premature to draft a detailed privacy policy it, the company said.

“The services authorized by the agreement haven’t been built or even designed yet,” Dan Clancy, engineering director for Google Books, wrote. “That means it’s very difficult (if not impossible) to draft a detailed privacy policy. While we know that our eventual product will build in privacy protections — like always giving users clear information about privacy, and choices about what if any data they share when they use our services — we don’t yet know exactly how this all will work. We do know that whatever we ultimately build will protect readers’ privacy rights, upholding the standards set long ago by booksellers and by the libraries whose collections are being opened to the public through this settlement.”

Cindy Cohn, legal director at the Electronic Frontier Foundation, said that she decided to go ahead with the public campaign after months of discussions with Google. She said that Google’s response was insufficient and that the company should commit to guarantees in writing before the settlement is reviewed by a court in October. And she dismissed the argument that Google could not make privacy guarantees until the product was built.

“Whether to hand data only in response to a warrant or not is not a tech decision,” she said in an interview. “Whether you are holding data for 30 days or longer is not a tech decision.”

Other groups, including the American Library Association, have also raised concerns about privacy and have asked the court to exercise vigorous oversight of the settlement.