NEW YORK — A red-light district tentatively cleared for construction on the Internet — the “.xxx” domain — is being billed by backers as giving the $12 billion online porn industry a great opportunity to clean up its act.

A distinct online sector for the salacious, one with rules aimed at forbidding trickery, will reduce the chances of Internet users accidentally stumbling on porn sites, they argue.

If only it were so simple:

Zoning in cyberspace has always been a daunting proposition, and participation in the porn domain will be voluntary. Critics wonder why “.xxx” got the OK at all when so many other proposals sit unaddressed, some for years.

Nearly five years after rejecting a similar proposal, the Internet’s key oversight body, the Internet Corporation for Assigned Names and Numbers, voted 6-3 this month to proceed with “.xxx.”

ICANN staff will now craft a contract with ICM Registry Inc., the Jupiter, Fla., company that made the bid. If the board and ultimately the U.S. Commerce Department approve it, “.xxx” names could appear in use by the year’s end.

The market unquestionably exists: Two in five Internet users visited an adult site in April, according to tracking by comScore Media Metrix. The company said 4 percent of all Web traffic and 2 percent of all surfing time involved an adult site.

As envisioned, ICM would charge $60 for each of up to 500,000 names it expects to register, $10 of which would go to a nonprofit organization that would, among other things, educate parents about safe surfing for children.

The nonprofit, run by representatives of adult Web sites, free-speech, privacy and child-advocacy concerns, would determine registration eligibility.

Skeptics argue, however, that porn sites are likely to keep their existing “.com” storefronts, even as they set up shop in the new “.xxx” domain name. And that will reduce the effectiveness of software filters set up to simply block all “.xxx” names.

The “.xxx” domain “legitimizes this group, and it gives false hope to parents,” said Patrick Trueman, senior legal counsel at the Family Research Council and a former Justice Department official in charge of obscenity prosecutions.

The adult entertainment industry is also hardly behind “.xxx” as a group. Many of its webmasters consider the domain “the first step toward driving the adult Internet into a ghetto very much like zoning laws have driven adult stores into the outskirts,” said Mark Kernes, senior editor at the trade monthly Adult Video News.

ICM insists it would fight any government efforts to compel its use by adult Web sites, but the existence of “.xxx” would certainly make the prospect easier.

“There are going to be pressures” to mandate it once available, said Marjorie Heins, coordinator of the Free Expression Policy Project at New York University’s law school. Federal lawmakers have proposed such requirements in the past.

Robert Corn-Revere, a lawyer hired by ICM to address free-speech issues, said the company has pledged $250,000 for a legal defense fund to keep “.xxx” voluntary, and he notes that courts have struck down efforts to make movie ratings mandatory.

“Where governments have tried to use private labeling systems as proxies for regulation, courts have always held those measures unconstitutional,” he said.

Even if it’s voluntary, supporters say, adult sites will have incentives to use “.xxx.”

“If the carrot’s big enough, you’re going to get sites in there,” said Parry Aftab, an Internet safety expert who served as an informal adviser on “.xxx.”

Stuart Lawley, ICM’s chairman and president, said use of “.xxx” could protect companies from prosecution under a 2003 federal law that bars sites from tricking children into viewing pornography — as “.xxx” would clearly denote an adult site.

All sites using “.xxx” would be required to follow yet-to-be-written “best practices” guidelines, such as prohibitions against trickery through spamming and malicious scripts.

Lawley said those requirements could make credit-card issuers more confident about accepting charges. The online porn industry currently faces higher fees because some sites engage in fraud and customers often deny authorizing payments.

But given the limited effectiveness of a voluntary “.xxx” for filtering, Internet filtering expert Seth Finkelstein calls “.xxx” no more than a mechanism “to extract fees from bona fide pornographers and domain name speculators.” (ICANN also gets an unspecified cut of each registration fee.)

Even if it were mandatory, it wouldn’t be foolproof.

A domain name serves merely as an easy-to-remember moniker for a site’s actual numeric Internet address. David Burt, a spokesman for filtering vendor Secure Computing Corp., said a child could simply use the numeric address when the “.xxx” equivalent gets blocked.

Better technologies exist, he said, including a little-used self-rating system that lets Web sites broadcast whether they contain nudity, violence or foul language, along with the specific forms, such as presence of genitals or passionate kissing.

Burt also favors a “.kids” domain that would serve as a safe haven for children. The U.S. government has approved one under “.us,” but support has been cool, with only about two dozen “.kids.us” sites listed.

ICM proposed both “.xxx” and “.kids” in 2000, but ICANN board members resisted them for fear of getting into content control. Instead, ICANN approved “.info,” “.biz,” and “.museum” and four others.

But pressure has continued to mount for ICANN to expand the number of domain names, and last year it reopened bidding.

ICM resubmitted its application for “.xxx” only, this time structuring it with a policy-setting organization to free ICANN of that task.

That did the trick.

ICANN board member Joichi Ito, who backed “.xxx,” wrote in his Web journal that the decision wasn’t an endorsement of any type of content or moral belief but a chance for “creating incentives for legitimate adult entertainment sites to come together and fight ‘bad actors.”‘

Anti-porn activist Donna Rice Hughes, however, remains unconvinced.

“They are not going to give up their ‘.com’ addresses,” she said of porn sites. “It doesn’t take a brain surgeon to figure that one out.”