Social networking Web sites like MySpace and Facebook would have access to a database of sex offenders for checking names and addresses against public profiles under a bill introduced Tuesday in Congress.

The legislation, aimed at giving computer network operators the knowledge and ability to remove sexual predators from their sites, would require convicted sex offenders to register their e-mail addresses and other online identifiers with federal authorities. The information would not be released to the public.

Adults who misrepresent their age to a minor with the intent of sexually abusing a child could be prosecuted and sentenced to up to 20 years in prison.

"Lately, online predation is the method of choice for too many sexual predators," said Sen. Charles Schumer, D-N.Y. "We have to plug the online loophole."

The bill defines "social networking" sites in broad terms — a Web site that allows users to create public profiles and communicate with other users — and could include popular destinations like Amazon.com, which allows shoppers to make personal pages and discuss items for sale.

News Corp.'s MySpace, one of the most popular social networking sites, is backing the measure. "Our laws need to change with the times," said MySpace safety czar Hemanshu Nigam. "We're committed to making our corner of the Internet a safer and better lit neighborhood so that all of our users can feel and actually be safer."

Earlier this month, four families sued News Corp. after their daughters were sexually abused by adults they met on the site, alleging negligence, recklessness, fraud and negligent misrepresentation by the companies.

In December, MySpace announced a plan to develop technologies designed to help block convicted sex offenders by checking profiles against government registries. Requiring registrations of e-mail addresses would make matching easier.

There are more than 550,000 registered sex offenders in the United States. They are already required to register their physical whereabouts with the federal government.

The new law could be difficult to enforce — convicted sex offenders could easily use a computer at an Internet cafe to create an anonymous e-mail account and use it to register on a social networking site, for example — but the bill would make doing so a crime.