Law requires libraries to install filtering software on computers or risk losing millions of dollars in subsidies.

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Two soft-spoken, gray-haired librarians fired the opening salvo on Monday in a constitutional battle over how far the US government can go to protect children from exposure to pornography on library computers.

On trial before a special three-judge panel in US District Court is the Children's Internet Protection Act, or CIPA, a law that requires libraries to install filtering software on computers or risk loosing millions of dollars in subsidies that provide library patrons with Internet access.

The law is the third attempt by Congress to control online smut. Advocates say its narrow focus on federal funds for schools and libraries makes it the government's best shot thus far to restrict Internet access without violating free speech as protected by the First Amendment to the US Constitution.

The main problem, say librarians who are among plaintiffs suing to have the law overturned, is that the measure requires them to abandon their traditional role of providing adult patrons with access to lawful information and materials in an atmosphere that safeguards individual privacy.

"We really don't ask people why they want to know what they want to know," Ginnie Cooper, director of Multnomah County Public Library in Portland, Oregon, said in testimony as the nine-day trial got under way.

The American Civil Liberties Union and lawyers representing a coalition of libraries, library patrons, and website operators want the court to impose a permanent injunction against CIPA, saying the law not only violates the Constitution but imposes a costly and burdensome task on libraries.

Some critics view the measure as a ploy by social conservatives to restrict access to sites that discuss homosexuality and abortion rights.

But advocates say the law is necessary because an aggressive pornography industry is looking increasingly for ways to lure youngsters onto pornographic websites.

"I don't think there is a common definition as to what is hard-core pornography," said Candace Morgan, associate director of the Fort Vancouver Regional Library in Washington state, a plaintiffs' witness asked to examine color photos downloaded from a pornographic website.

"We have sex education manuals that have sexually explicit pictures similar to some of these," the grandmotherly figure with gray hair told the court. "The Hot-Teen... one? We have books on lesbian sex that could be similar to these, though they don't show teens."

Morgan and Cooper said their library systems provide blocking software on a voluntary basis and hold parents and guardians responsible for their children's activities. Both also have taken steps to protect bystanders from accidental exposure to objectionable material.

Both librarians testified that there were few complaints stemming from sexually explicit material viewed on library computers. In Portland, Cooper said, the library system received 11 Internet-related complaints during the year ended last July 1, the same number it received over the library board's decision to participate in the CIPA lawsuit.

But they acknowledged that the current system would allow underage children to access pornographic websites, and that in one case an adult was discovered looking at sexually explicit material on a computer in a library's children's section.

The first attempt by Congress to control online smut, the 1996 Communications Decency Act, was thrown out by the Supreme Court as an infringement of free speech. A second bid, the 1998 Child Online Protection Act, remains sidelined by an injunction, with the US high court due to issue a final opinion by midyear. Both would impose criminal penalties on violators.