Philadelphia- A porn trial without dirty pictures.

That’s what’s playing out in a courtroom on the 17th floor of the federal courthouse in Center City, where a drawn-out First Amendment case is being heard.

At issue is the Children Online Protection Act, or COPA, a law Congress enacted in 1998 but never enforced as it bounced all the way up to the Supreme Court and back down again.

Plaintiff: the American Civil Liberties Union, et al. Defendant: the attorney general of the United States.

U.S. District Judge Lowell A. Reed Jr. is hearing the case without a jury and will decide whether the law aimed at keeping children from accessing Internet porn should stand, be modified or fall.

And with no dirty pictures – Reed has ruled against their display – the trial has become something of a wonk’s drama, a battle of experts, including a university philosopher, talking about Internet filters and online commerce.

The ACLU, whose witnesses have included artists and online writers, argues that the law is overreaching and that parents have access to filters and other measures – such as monitoring their children’s Internet activities and educating them about the dangers of the Web – to protect minors.

The government counters that many households do not have filters and that filters themselves are not foolproof.

And in a twist, the government also maintains that none of the plaintiffs, including the online magazine Salon.com, the sex advice site scarleteen.com, and the merchant site condomania.com, would be covered by COPA.

The law would authorize jail time and heavy fines for online smut merchants who do not require adult-access codes, personal identification, or credit cards to access their Web sites.

The ACLU says that even some minors have credit cards and that such a requirement discriminates against adults who do not have plastic.

Last week, one of the defense witnesses was Stephen Neale, a Rutgers University professor of philosophy who specializes in linguistics. Speaking sometimes very quickly in an English accent, Neale had to repeat from time to time what he had said so the court reporter could get it down.

Hired by the government as an expert witness at $300 an hour, Neale had studied Internet filter programs that rely on text on, or imbedded in, sites to weed out porn.

Describing the Web as “huge,” Neale said no filter could ever succeed in stopping every porn site and that filters also run the risk of blocking legitimate sites for such things as breast cancer.

On a screen, Justice Department attorney Raphael Gomez put up a section of Neale’s report that listed words that have double meanings and that could result in a clean site’s being blocked.

Asked on cross-examination what might work to block all porn sites, Neale said: “Pulling the plug on the Web is the only thing I can think of.”

Judge Reed had issued an injunction against the law in 1999, saying there was a “substantial likelihood” it violated First Amendment protections. The Supreme Court upheld that decision, 5-4, in 2004. But the high court ordered a trial to allow the government to consider less-restrictive alternatives – such as Internet filters – or to show that the law is a reasonable restraint on free speech.

In his opening argument, ACLU attorney Chris Hansen said neither side would claim that Internet filters or the law were “perfect.”

But, he added later, “almost by a startling percentage, filters are significantly more effective than COPA would be.”

Opening for the defense, government attorney Eric Beane said the only beneficiary of the injunction blocking the enforcement of COPA had been the hard-core smut industry.

“The ACLU, in its zeal to prevent the government from hypothetical and highly improbable overregulation, would cause the real problem – those pornographic Web sites – to remain unregulated,” Beane said.

The trial, which began Oct. 23, is expected to run until the end of the month, with Reed issuing a decision sometime after that.