Some Democrats in the House and the Senate, however, have already embraced the idea of a do-not-track mechanism. On Thursday, Representative Ed Markey, a Massachusetts Democrat, said he would introduce a bill that would put in place such a system to prevent the tracking of children using the Internet.
At a House subcommittee hearing on Wednesday, Republicans generally expressed caution with varying degrees of support for stricter privacy measures. “We need to be mindful not to enact legislation that would hurt a recovering economy,” said Representative Ed Whitfield of Kentucky, the leading Republican on the House Subcommittee on Commerce, Trade and Consumer Protection.
“While I agree it is important to have consumers understand what information is being collected and how it is used,” Mr. Whitfield said, “we need to seriously discuss the do-not-track model and evaluate whether it accomplishes the appropriate objectives.”
Officials from the trade commission and the Commerce Department, which is preparing its own report about online privacy for release before the end of the year, said that they had not yet seen examples of enhanced privacy measures affecting advertising revenues.
“There are more and more companies that are offering users some kind of opt-out, enhanced-notice mechanism, and I don’t believe we’ve seen dramatic fall-off of advertising revenues as a result,” said Daniel J. Weitzner, associate administrator for policy at the National Telecommunications and Information Administration, a bureau in the Commerce Department that is preparing the report.
He acknowledged that caution was required. “I think that there are mechanisms that could be mandated that could have a dramatic impact on advertising,” Mr. Weitzner added.
Some companies that sell advertising agreed. Joan Gillman, an executive vice president at Time Warner Cable , said in a statement to the subcommittee that “do-not-track could hinder job creation within the advertising industry and by Web sites that rely on advertising revenues,” as well as “inhibit innovation and the development of new services.”
But Susan Grant, the director of consumer protection at the Consumer Federation of America, said that the type of all-encompassing surveillance becoming increasingly common online would rarely be tolerated.
“If someone were following you around in the physical world — tailing you and making note of everywhere you go, what you read, what you eat, who you see, what music you listen to, what you buy, what you watch — you might find this disturbing,” she said.
“On the Internet,” she added, “even if the tracker doesn’t know your name, you are not anonymous.” She pointed to technology like so-called cookies and other persistent, digital identifiers that “are essentially personally identifying information.”
Putting in place a do-not- track system would probably require Congressional action. Mr. Whitfield and others also raised questions about whether the government was the best party to devise and put in place a do-not-track system. He also suggested that the collection of information about people who do not want to be followed online would itself create new privacy problems.
David Vladeck, director of the trade commission’s bureau of consumer protection, responded to that concern by saying that the government would not need to be involved in managing such a system; it would only enforce its requirements.
“We’re not proposing the creation of a list,” Mr. Vladeck said. “Nor are we proposing a centralized system managed by the federal government. While the Federal Trade Commission must be able to ensure through enforcement that a do-not-track mechanism effectively implements consumer choice, there is no need for it to be administered by the federal government.”
In addition, a do-not-track feature would be different from the national do-not-call registry in significant ways, Mr. Vladeck said. While the do-not-call registry uses a phone number as a unique identifier, there exists no such identifier for computers. Internet protocol addresses can change frequently, and consumers typically use multiple devices and Internet service providers to access online content.
There have been hints of broader support among House Republicans for stricter privacy measures, including from Representative Joe L. Barton of Texas, currently the ranking Republican on the House Energy and Commerce Committee and who is expected to be a strong contender to become chairman of the committee.
“I want the Internet economy to prosper, but it can’t unless the people’s right to privacy means more than a right only to hear excuses after the damage is done,” Mr. Barton said in a statement issued after the F.T.C. released its report on Wednesday. “In the next Congress, the Energy and Commerce Committee and our subcommittees are going to find out if Internet privacy policies really mean anything, and if necessary, how to make them stick.”