Concerned by the wave of requests for customer data from law enforcement agencies, Google last year set up an online tool showing the frequency of these requests in various countries. In the first half of 2010, it counted more than 4,200 in the United States.

Google is not alone among Internet and telecommunications companies in feeling inundated with requests for information. Verizon told Congress in 2007 that it received some 90,000 such requests each year. And Facebook told Newsweek in 2009 that subpoenas and other orders were arriving at the company at a rate of 10 to 20 a day.

Many Internet companies and consumer advocates say the main law governing communication privacy — enacted in 1986, before cellphone and e-mail use was widespread, and before social networking was even conceived — is outdated, affording more protection to letters in a file cabinet than e-mail on a server.

They acknowledge that access to information is important for fighting crime and terrorism, but say they are dealing with a patchwork of confusing standards that have been interpreted inconsistently by the courts, creating uncertainty.

Last year, for example, the Justice Department argued in court that cellphone users had given up the expectation of privacy about their location by voluntarily giving that information to carriers. In April, it argued in a federal court in Colorado that it ought to have access to some e-mails without a search warrant. And federal law enforcement officials, citing technology advances, plan to ask for new regulations that would smooth their ability to perform legal wiretaps of various Internet communications.