The California Supreme Court showed little inclination Tuesday to allow suits against Internet service providers such as Google and Yahoo by people who claim they were libeled online.

The court is reviewing an October 2003 ruling by a state appeals court that a service provider is responsible for the contents of a defamatory message if the provider knew, or had reason to know, that the message was libelous and failed to remove it.

That's the standard that applies to other media -- for example, a newspaper that continues to run an advertisement, or a publisher that distributes a book, after learning of their libelous content. But every other court that has considered the issue has ruled that federal law makes Internet providers immune from such suits, and most of the state Supreme Court justices at Tuesday's hearing appeared to agree.

"The Internet is just different," Justice Carol Corrigan said. "This isn't a publishing house," she said, but a medium that serves its users by posting their messages without interference.

Chief Justice Ronald George asked how the Internet could function if providers had to investigate the truthfulness of the messages they displayed. Justice Joyce Kennard noted that plaintiffs can sue the authors of libelous messages or post their own replies online. Justice Ming Chin said there was a "startling lack of legal authority" for such suits.

But plaintiffs lawyer Christopher Grell said the Internet could be preserved as a forum "without requiring the total sacrifice of a person's reputation." Victims of anonymous but widely disseminated smears would have no recourse, he said, if they couldn't sue Internet service providers.

A ruling is due within 90 days.

The case, from Alameda County, does not involve a conventional Internet service provider but instead focuses on the responsibility of a person who took allegedly libelous messages from a third party and distributed them to online newsgroups.

The plaintiffs are physicians who say they were libeled by hundreds of messages that Ilena Rosenthal, an advocate of alternative health care, got from another source and posted from 1999 to 2001. One plaintiff said he had told Rosenthal that one message falsely accused him of criminal conduct, but she repeated it in 32 postings.

Rosenthal sought dismissal of the suit under a 1996 federal law that says providers of Internet chat rooms or news groups are not considered the publisher of information provided by others.

Federal and state courts had consistently interpreted the law as protecting Internet service providers from suits over messages, until the 2003 ruling by the state Court of Appeal in San Francisco that reinstated the suit against Rosenthal. The court said the federal law was intended to encourage service providers to monitor the messages they carried.

At Tuesday's hearing, Ann Brick, an American Civil Liberties Union lawyer siding with Rosenthal, said the appeals court's interpretation would discourage monitoring and self-regulation. To avoid responsibility for libel, she said, an Internet provider would "make sure it knows as little as possible" about the messages it carried.

The case is Barrett vs. Rosenthal, S122953.