(PHILADELPHIA, PA) -- Three soft-spoken, gray-haired librarians fired the opening salvo on Monday in a constitutional battle over how far the U.S. government can go to protect children from exposure to pornography on library computers.

As an unusual constitutional trial opened in U.S. District Court, librarians from Wisconsin, Oregon and Washington warned that the Children's Internet Protection Act could undermine the role of American libraries that seek to provide adult patrons with any lawful material regardless of content or viewpoint.

"We really don't ask people why they want to know what they want to know," Ginnie Cooper, 56, director of Multnomah County Public Library in Portland, Oregon, testified in what is expected to be a nine-day trial.

Known by the acronym Cipa, the law is a third attempt by Congress to restrict access to the Internet and its estimated 11 million World Wide Web sites, about 1 percent of which experts say contain some sort of sexually explicit material.

Cipa, signed into law in 2000 by then-U.S. President Bill Clinton, would require libraries to install filtering software on computers or risk loosing millions of dollars in subsidies that provide library patrons with Internet access.

Because it does not directly impose limits on Internet access, supporters view Cipa as the government's best shot yet at controlling online smut while avoiding violations of the free speech rights guaranteed by the First Amendment to the U.S. Constitution.

But the American Civil Liberties Union (news - web sites) and lawyers representing a coalition of libraries, library patrons and Web site operators want a special three-judge panel to impose a permanent injunction against Cipa, saying it violates free speech rights and imposes costly burdens on libraries that would be forced to comply.

The verdict by the judicial panel headed by 3rd U.S. Circuit Court of Appeals (news - web sites) Chief Judge Ed Becker will go directly to the U.S. Supreme Court (news - web sites).

Despite the free speech issues raised by the trial, Becker ordered the courtroom closed to the public briefly during expert testimony that could divulge trade secrets about specific filtering software products.

The chief judge noted that the courtroom's closure could raise concerns that the law should be overturned on grounds that it could not be defended wholly in a public courtroom.

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, the 1998 Child Online Protection Act, remains sidelined by an injunction with the U.S. high court due to issue a final opinion by mid-year. Both would impose criminal penalties on violators.

Filtering Software Faulty?

A main objection to Cipa among librarians is a section that would require adult patrons to ask that filtering software be shut off for what the statute calls "bonafide research."

"I really myself have no idea how I would say to someone: 'Why do you want this?'," said Peter Hamon, 56, director of Madison, Wisconsin's South Central Library System.

Plaintiffs in the case, who have named the Federal Communications Commission (news - web sites) and the Institute of Museum and Library Sciences as defendants, also maintain that filtering software is faulty in two ways -- it either blocks Web sites that are not objectionable or allows access to some that are.

"None of the programs currently available can accomplish their stated task of filtering out sexually explicit material," testified Geoffrey Nunberg, a Stanford University linguistics professor who studied several software products on the market.

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