WASHINGTON – Commercial Web-site operators who publish sexually explicit or pornographic material would be required to place official government warning marks or labels on their sites or face up to five years in prison, under a bill by Arizona GOP Sen. Jon Kyl.

Those warnings would enable parents and other Internet users to filter such pages.

Sexually explicit material also could not appear on a site’s first page or home page, requiring additional steps by the Internet visitor to view the explicit content.

Similar punishment would face pornographers who camouflaged the source coding of their Web sites, including hiding key words like the brand names of popular toys, so those sites pop up more frequently through Internet search engines such as Google.

But free-speech advocates say the new bill, which would require the Federal Trade Commission to develop the new warning notices for sexually explicit Web pages, is too sweeping. They say Internet expression is entitled to the same constitutional protections as other media.

Much of the Stop Adults Facilitating the Exploitation of Youth Act, or Internet SAFETY Act, introduced by Kyl on Tuesday, is based on recommendations of the Justice Department. In May, the department issued a report declaring that the Internet is helping to fuel “an epidemic of child pornography.”

“It is a fairly descriptive acronym, for the provisions of the Internet SAFETY Act are designed to crack down on the spread of Internet child pornography and related conduct,” Kyl said in remarks for the Congressional Record.

The Justice Department noted in its report that the Internet, by providing greater technical ease and increased anonymity in trading images, has “taken down barriers that one time served as a deterrent to child pornographers.”

To combat this, Kyl’s bill creates tougher penalties and a broader array of federal charges that could be brought against Internet producers and distributors of child pornography.

It also increases criminal penalties for sex trafficking and sexual-abuse offenses and authorizes more resources, including 200 new assistant U.S. attorneys, to prosecute child sexual-abuse offenses.

But some question the bill’s constitutionality.

“There’s nobody who should like child pornography, and no one is going to defend child pornographers,” said David Greene, executive director of the Oakland-based First Amendment Project, a non-profit organization that litigates and researches free-speech issues.

But Greene, also a founding member of the Internet Free Expression Alliance, took issue with the effort to require official government warning labels for commercial Web sites with “sexually explicit” content.

He said that requiring such labeling would face constitutional problems on grounds that it is impermissible compelled speech and “might kill an otherwise perfectly fine bill.”

The ratings system now used by the movie industry is voluntarily enforced and functions without the threat of criminal penalties.

But under Kyl’s new bill, Web-site operators who didn’t include warning marks on sites containing sexually explicit material would face up to five years in prison.

The offense would apply only to commercial Web-site operators and would require prosecutors to prove that the operator knew the material was on the site.

For a definition of “sexually explicit,” the bill borrows from existing federal law. It covers sexual intercourse, bestiality, masturbation, sadistic or masochistic abuse, or lascivious exhibition of the genitals or pubic area of any person.

But Greene said courts have broadly interpreted some of those definitions.

Kyl’s office said the proposed warning marks that the FTC would develop would not serve the function of “ratings” but would simply inform a viewer that the Web site contained sexually explicit material and help parents or others to filter the pages.

A pornographer who hides terms in a Web site’s source coding to trick people into viewing “obscene material” also could face up to 10 years in prison or up to 20 years if the intent was to specifically target children into viewing pornography on the Internet.

From 1998 to 2004, child-pornography reports made to the National Center for Missing and Exploited Children increased to 106,119 from 3,267.

The Justice Department also has noted that there has been an escalation in the severity of abuse depicted in child pornography in recent years, “with the images found today more frequently involving younger children, including toddlers and even infants, and despicable acts such as penetration of infants.”

Co-sponsors of the bill are Sens. John Cornyn, R-Texas; George Allen, R-Va.; Conrad Burns, R-Mont.; Kay Bailey Hutchison, R-Texas; Olympia Snowe, R-Maine; Mike DeWine, R-Ohio; Charles Grassley, R-Iowa; and Sam Brownback, R-Kansas.