WASHINGTON — When the Supreme Court first considered the constitutionality of a law regulating the Internet in 1997, some of the justices needed a demonstration from their law clerks and the Court's library to figure out what the Internet was.

But yesterday, when the Court heard arguments in its third case on the subject, the justices seemed well-versed in Internet shopping, Google searches and the multi-layered nature of many Internet sites.

For First Amendment advocates, however, that familiarity may not be a positive development in some instances, because justices have also learned how easy it is to access Internet pornography.

The Court heard arguments in Ashcroft v. ACLU II, its second look at the latest attempt by Congress to regulate children's access to online material that is "harmful to minors." The Child Online Protection Act, or COPA, which focuses on commercial sites that traffic in adult material, was passed the year after the Court struck down the first, broader law, the Communications Decency Act, in 1997 in Reno v. ACLU. The 3rd U.S. Circuit Court of Appeals struck down the new law too, and when the high court first reviewed COPA, it sent the case back to the 3rd Circuit. That court again found the law unconstitutional, so once again the law is before the Supreme Court.

Overall, the justices were relatively quiet — Justice David Souter, uncharacteristically, asked no questions at all — suggesting that the Court may have tired of the subject, and may possibly be willing to give Congress the benefit of the doubt on the law.

Solicitor General Theodore Olson made a strong pitch for the law, telling the justices more than once that Congress had carefully drafted it to meet the Supreme Court's objections on the first law and to avoid its constitutional flaws. The problem of Internet pornography was an ever-increasing "menace," he said, because the material is "pervasive and essentially unavoidable."

As an example, he said that when he typed the words "free porn" into his home computer's search engine last weekend, it found 6,230,000 sites. When Justice John Paul Stevens asked rhetorically if all those sites were obscene, Olson replied sarcastically that he "didn't have time to see them all."

Spectators laughed, but the exchange also indicated that some justices are still concerned that the law bans material that is well outside the definition of obscenity. The Court has long held that obscenity — appealing to prurient interests and without redeeming social or artistic value — is not protected by the First Amendment. But the justices get nervous when government tries to restrict speech outside that definition, especially when they are not convinced that less intrusive methods have been tried. Justice Sandra Day O'Connor struck that theme, telling Olson that she wonders why the obscenity laws pertaining to adults are not enforced very vigorously. "What's going on?" she asked accusingly.

Olson, clearly referring to the Clinton administration, acknowledged that there had been few obscenity prosecutions "a few years ago," but that the pace of prosecution was picking up.

Olson also repeatedly drew an analogy between the law at issue and older statutes that require adult magazines to be displayed in stores in "blinder racks" that obscure their covers to prevent children from seeing them. But Justice Ruth Bader Ginsburg challenged the analogy, noting that the Internet law requires vendors to force customers to use a credit card or some other form of adult identification before accessing a site. "I don't have to give my ID" at a bookstore, Ginsburg said.

Justice Anthony Kennedy also dismissed the bookstore analogy, telling Olson, "We know about books. Web sites are different. We are struggling."

At this point in the oral argument, it appeared that the skeptics outnumbered the supporters of the law. But then American Civil Liberties Union lawyer Ann Beeson rose to challenge the law, and she too got a lot of skeptical questioning.

Beeson argued that the law, with its criminal penalties, would chill or punish a wide range of speech that should be protected by the First Amendment. "If you self-censor material that is harmful to minors, you are censoring material that adults have a right to see."

But Justice Stephen Breyer repeatedly challenged her to provide examples of legitimate sites that would be censored by the law. She cited sex advice columnists and gay and lesbian sites, but Breyer said none of those would appear to be covered by the law, because they had some redeeming value and probably did not merely appeal to prurient interests.

Beeson also argued, picking up on O'Connor's questioning, that less-restrictive means had not been adequately tried. She said that prosecuting purveyors under existing obscenity laws could work, and she also mentioned the law requiring libraries to filter their computers to restrict access to adult materials.

That drew criticism from Chief Justice William Rehnquist and Justice Antonin Scalia, who noted that the ACLU had challenged these and other less-restrictive laws as well. When Beeson cited another recent law that penalizes sites with misleading domain names — such as www.whitehouse.com, which is an adult site — Scalia sarcastically tried to win assurance from Beeson that the ACLU would not challenge it. "We can count on that one being O.K.?" Scalia said. Beeson made no promises.

Beeson ended with a plea to preserve the Internet as a wide-open medium, a characteristic that the Court praised in its initial ruling in 1997. "The value of this medium is its extremely low barriers to entrance," Beeson said. "By setting up these barriers, you can destroy the nature of the medium."