Internet companies fear that because the definitions of terms like “search engine” are so broad in the legislation, Web sites big and small could be responsible for monitoring all material on their pages for potential violations — an expensive and complex challenge.

They say they support current law, which requires Web sites with copyright-infringing content to take it down if copyright holders ask them to, leaving the rest of the site intact. Google, which owns YouTube and other sites, received five million requests to remove content or links last year, and it says it acts in less than six hours if it determines that the request is legitimate.

The major players supporting the legislation, including the United States Chamber of Commerce and the Motion Picture Association of America, say those measures are not enough to protect intellectual property. They emphasize that their primary targets are foreign Web sites that sell counterfeit goods and let people stream and download music and video at no charge — sites that are now largely out of reach of United States law enforcement. And they are fighting against what they characterize as gimmicks and distortions by Internet companies opposed to the bills.

With talk of censorship and loss of Internet freedom, “the current debate has nothing to do with the substance of the bills,” David Hirschmann, who leads the Chamber of Commerce’s initiative on intellectual property, said in an interview. “We will certainly use every tool in our toolbox to make sure members of Congress know what’s in these bills.”

With financial resources that few other groups can match, the chamber is one of Washington’s most powerful lobbying forces and has shown the ability to alter Congressional debate on its own.