WASHINGTON — Six years after Congress passed the Child Online Protection Act, the Supreme Court still has not decided whether the law's Internet restrictions are constitutional. And by the time it looks at the law again, the Supreme Court's composition may have changed.

That is the upshot of yesterday's Supreme Court ruling that for a second time sent the law back to lower courts for more study. Its 5-4 ruling, Ashcroft v. ACLU II, issued just before adjourning for the summer, sends the case back to the federal District Court in Philadelphia for further scrutiny of the "plausible, less restrictive alternatives" to the law, which makes it a crime for commercial Web sites to place adult material on the Internet where it can be viewed by minors.

In the meantime, Justice Anthony Kennedy wrote for the majority, the injunction that has halted enforcement of COPA since it was signed into law in 1998 should remain in effect.

The Court, while putting off resolution of the dispute yet again, used language in the decision that was heartening to First Amendment advocates. The language may also guide the lower court's examination in a way that increases the chances that, once again, the lower court will find the law unconstitutional. The case could return to the high court a year or more from now.

Kennedy wrote that "[c]ontent-based prohibitions, enforced by severe criminal penalties, have the constant potential to be a repressive force in the lives and thoughts of a free people. To guard against that threat the Constitution demands that content-based restrictions on speech be presumed invalid and that the Government bear the burden of showing their constitutionality."

But Kennedy also let it be known that the law could be found constitutional. "This opinion does not foreclose the district court from concluding, upon a proper showing by the government … that COPA is the least restrictive alternative to accomplish Congress' goal."

More broadly, Kennedy also reassured Congress that it may have a legitimate role to play in Internet regulation. "It is important to note that this opinion does not hold that Congress is incapable of enacting any regulation of the Internet designed to prevent minors from gaining access to harmful materials."

American Civil Liberties Union lawyer Ann Beeson, who argued against the law before the Court, said yesterday, "By upholding the order stopping Attorney General (John) Ashcroft from enforcing this questionable federal law, the Court has made it safe for artists, sex educators, and Web publishers to communicate with adults about sexuality without risking jail time." She also called on Ashcroft not to spend any more taxpayer dollars to defend the law.

Justice Department spokesman Mark Corallo voiced disappointment in the ruling. "Congress has repeatedly attempted to address this serious need and the Court yet again opposed these common-sense measures to protect America's children. The Department will continue to work to defend children from the dangerous predators who lurk in the dark shadows of the World Wide Web," he said in a statement.

The ruling is the latest chapter in the history of congressional attempts to protect minors from objectionable Internet content.

After the Supreme Court in its 1997 ruling in Reno v. ACLU found the Communications Decency Act unconstitutional, Congress tried again to find a way to restrict minors' access to sexually explicit material on the Internet.

The result was COPA, which makes it a crime, knowingly and for commercial purposes, to make any material that is "harmful to minors" accessible to minors. "Harmful to minors" was defined as anything that is either obscene or by community standards appeals to prurient interests, depicts sex acts or genitals, or lacks artistic merit, among other definitions.

Before it could take effect, the law was found unconstitutional at both the district court and appeals court levels and was enjoined from being enforced. In 2002, the Supreme Court examined the law and returned it to the appeals court for further findings on whether the injunction was justified. In its ruling, Ashcroft v. ACLU, the Supreme Court said the use of the "community standards" rule in the law was not overbroad under the First Amendment. In its second look at the law, the 3rd U.S. Circuit Court of Appeals again found the law was not narrowly tailored and was overbroad and therefore unconstitutional.

Kennedy wrote that the district court was acting properly in enjoining enforcement of the law because of its likely First Amendment problems.

The ruling focused on only one of these problems — whether less-restrictive means exist to achieve the law's objectives. "The purpose of the test is to ensure that speech is restricted no further than necessary to achieve the goal, for it is important to assure that legitimate speech is not chilled or punished," Kennedy wrote.

Filtering alternatives that are available to parents, Kennedy suggested, are less restrictive than COPA because they "impose selective restrictions at the receiving end, not universal restrictions at the source." He also cited research indicating filters may be more effective in restricting minors' access to adult material generated overseas, beyond the reach of the law.

But Kennedy also noted such software is "not a perfect solution," in that it sometimes blocks material appropriate for children, while letting through adult material that should be blocked.

Noting the "rapid pace" of technological change, Kennedy also suggested that court scrutiny of Internet regulation is likely to lag behind reality. Kennedy described this gap as "a serious flaw in any case involving the Internet." But he said that by remanding the case back to the trial-court level, the Court was enabling the parties to update their case records with any new technological advances.

A frustrated Justice Stephen Breyer, writing in dissent, reviewed the history of the law and asked, "What else was Congress supposed to do?" He said Congress had read the Supreme Court's Reno decision "with care" and shaped its second legislative effort to respond to its criticisms.

Breyer, joined by Chief Justice William Rehnquist and Justice Sandra Day O'Connor, called the law's scope "modest" and constitutional. Justice Antonin Scalia also dissented, claiming that the law should not be subjected to higher-level "strict scrutiny" but instead could be easily justified under lesser standards.