An appeals court put on hold a long-running lawsuit over Google's massive book-scanning project Monday, likely delaying a full hearing on the merits of the copyright issues in the case.

The US appeals court overruled a circuit judge who last month called for a hearing to go forward even as Google contested whether the case may be certified as a class action.

The appeal judges granted Google's motion to delay a hearing at the lower court, noting that the groups suing the Internet giant had indicated "that they consent to the stay, although not to the arguments put forward in the motion as to why Google expects to prevail on appeal."

The Authors Guild and the Association of American Publishers filed the suit in 2005 alleging copyright infringement in Google's effort to digitize millions of books to be made available online.

As a result of Monday's order, the appeals court will first decide if the case should be heard as a class action. After that is resolved, the matter may proceed in the lower court, possibly to trial.

The US tech giant has argued that its Google Books project should be considered "fair use" under copyright law, and that the digitized versions are not a substitute for the books themselves.

Google has scanned more than 20 million books so far in the project.

Books in the public domain -- without current copyrights -- are made available online to the public for free. For copyrighted books Google offers a searchable database that displays snippets of text.

A tentative settlement in the case was reached in 2008 under which Google would pay $125 million to resolve copyright claims and to establish an independent "Book Rights Registry." But a judge rejected the deal.

Opponents of the agreement have said allowing Google to proceed with the project raises anti-trust, privacy and copyright issues, while also granting sole rights to Google to digitize millions of out-of-print works whose authors cannot be traced.

Others say copyright cannot be waived unless an author expressly opts out of the deal.