Just after the big March 19 argument at the Supreme Court on the constitutionality of the Communications Decency Act-which makes it a federal crime to "display . . . patently offensive," sexually explicit words or pictures on the Internet "in a manner available to a person under 18"-I was interrupted by a phone call while perusing the plaintiffs’ brief.

It was my Internet-cruising, 12-year-old daughter, Sarah. She burst in while I was rereading the part about how the best way to protect our kids from wandering into the pit of Internet smut is not government censorship or regulation, but the sort of parental control software that you can install on your home computer or get for free through services like America Online.

"Dad," demanded Sarah, "what have you done to America Online?"

Uh-oh. What I had done, inspired by the litigation, was to activate the "parental controls," by clicking on various boxes that did things I little understood.

"You’ve ruined it," Sarah complained. "I need the IMs. That’s the funnest part. Dad, you can trust me."

IMs? Huh? I turned off the IMs? What the hell are IMs, anyway? (Instant messages, it turns out.) In any event, it seems that the "parental controls" had not only slammed the door on the smut peddlers, and the art museums displaying racy nudes by Mapplethorpe and classy ones by Michelangelo, and the like; they had also shut Sarah off from private, real-time discussion groups with her online buddies. (Here’s hoping they’re all really kids, like they claim to be.) So now there will be no peace in my home until I undo the parental controls (pending further study of whether I can fine-tune them), swinging the doors open to the whole vast, anarchic, wonderful, variegated, democratic, interactive, participatory Internet-porn and all.

In doing so, Deputy Solicitor General Seth Waxman had suggested that morning in his well-crafted oral argument for the government in Reno v American Civil Liberties Union, I will be giving my kids "a free pass to the equivalent of every adult bookstore and video store in the country"-a veritable cornucopia of sex, bestiality, S&M (not to be confused with IMs), filth, scum, trash, and worse, just a few clicks of the mouse down the information superhighway.

That’s why, Waxman suggested, the Court should uphold the Communications Decency Act (CDA), which is Congress’ best effort (so far) to keep Internet pornography and other "indecent" materials away from kids whose parents cannot or will not do the job themselves.

It’s nice of Congress to want to help. And the arguments for some sort of governmental regulation to shield kids from Internet smut are stronger than most of the CDA’s legion of libertarian critics like to admit.

One of those arguments turns First Amendment values against the First Amendment champions: "Much of the Internet’s vast potential as an educational and informational resource will be wasted," the government’s brief contends, if parents fear that letting the Internet into their homes will expose their kids to a world of online smut.

But Congress has a way of overdoing things. And this slapdash, sloppily drafted, vague, overbroad blunderbuss of a statute, which was adopted without even a hearing to explore its far-reaching chilling effects on constitutionally protected speech, is a prime example. In making it a crime to post "indecent" speech anywhere on the Internet that kids might roam, the act makes it risky not just to peddle porn, but also for libraries, advocacy groups, and other nonprofits to display sexually explicit art or graphic sex-education materials; for individuals engaged in spirited online debate to toss in a four-letter word; for kids to gossip among themselves about sex; and much more.

Consider the four-letter word that got me in trouble with America Online’s in-house cybercops. My 12-year-old, while being flamed in a chat room by some other kid, rashly resorted to the raunchiest retort that came to mind: "fart-nugget." This I discovered to my horror (tinged with amusement) when I received a warning in my e-mailbox that my America Online "account" had been observed engaging in unacceptable indecency.

The question arises: Was it a federal crime for Sarah to transmit "fart" to another kid? Probably not. They don’t prosecute 12-year-olds, do they? But suppose that Sarah were 17 and had used a somewhat stronger Anglo-Saxon monosyllable, or a bunch of them. The legislative history of the CDA indicates that Congress intended to cover things like comedian George Carlin’s "seven dirty words" monologue, which the Supreme Court had found to be "indecent" in FCC v. Pacifica Foundation (1978); the Court upheld an FCC rule banning radio broadcasts of such stuff during daytime hours, when lots of kids would likely be listening. "Fart" was not one of Carlin’s seven dirty words, but it was in his top 20. How dirty is too dirty?

Or take the question that Justice Stephen Breyer asked Waxman at oral argument, hypothesizing a bunch of high school kids who get together in one of those private Internet chats and boast about their sexual exploits, "real or imagined." Are they all committing federal crimes? Breyer asked.

Waxman’s answer was not exactly no, honest fellow that he is. Breyer seemed not to find that reassuring. Nor, apparently, did Justice David Souter, who tossed in a hypo about a parent allowing his teen-ager to use the parent’s computer to access possibly "indecent" Internet materials. "The parent would also go to prison, I take it?" Souter asked. Waxman didn’t think so, but he couldn’t deny that a literal interpretation of the statute could theoretically support such a prosecution.

The oral argument, however, was not exactly a slam-dunk for Waxman’s equally adept adversary, D.C. lawyer Bruce Ennis of Jenner & Block, representing a broad coalition including the American Library Association, the ACLU, America Online, Microsoft, nonprofit health and educational groups, and some 40 others. While Ennis stressed the uniquely "democratizing and speech-enhancing" potential of an uncensored Internet, justices peppered him with analogies to Court decisions upholding restrictions of "indecent" speech in other media-bookstores, cable, and dial-a-porn services, as well as broadcast-So protect children.

Ennis central point was that the CDA would operate essentially as a ban on a wide range of constitutionally protected but arguably "indecent" speech on the Internet-excepting, ironically, the large percentage of Internet smut that comes from abroad, which the CDA apparently would not touch. His factual premise was that it is either technologically impossible or prohibitively costly for the vast majority of Internet speakers to check the ages of visitors to their sites and thus to exclude children.

But that conclusion-albeit accepted by the lower court in its findings of fact-may or may not hold true for very long. Waxman suggested that inexpensive age-verification options are becoming available. And Justice Antonin Scalia, stressing the rapid pace of change in computer technology, told Ennis that the factual record on which the lower court’s findings were based may already be obsolete, and that "this case depends on who has the burden of proof" on how broadly the CDA would in fact chill protected speech in the long run. Scalia suggested that the burden should be on Ennis and others who claim that the statute would in practice amount to an unconstitutionally broad regime of censorship, and that they have not carried it.

Scalia seems wrong about that. When Congress enacts a censorship regime with heavy criminal penalties for violating an extremely vague prohibition of "indecency," without taking the trouble to explore what its effects might be or to create a factual record; and when the best currently available evidence suggests that this regime will in fact banish a wide range of constitutionally protected speech from most portions of a vast, rapidly expanding, dynamic new communications medium frequented by millions of adults; and when Congress stated goal of keeping kids away from smut will apparently be undermined by a flood of easily accessible smut from abroad; and when home-based parental controls are available, even to those of us who have trouble using them, then the Court’s job is to strike down that regime of censorship.

In doing so, the justices should not close the door to more narrowly tailored legislation to shield kids from Internet smut, especially the kind peddled by commercial enterprises, which already obtain credit card numbers from viewers for their own purposes and thus can easily satisfy the CDA’s age-verification provisions.

But the Court should also make it clear that the kind of "uninhibited, robust, and wide-open" debate that it found to be protected in New York Times v. Sullivan (1964), in all of its (sometimes "indecent") forms, cannot be banished from what one of the judges on the panel below, U.S. District Judge Stewart Dalzell, aptly called the "never-ending worldwide conversation" that the Internet has the potential to be.