WASHINGTON - Federal law enforcement and national security officials are preparing to seek sweeping new regulations of the Internet, arguing that their ability to wiretap criminal and terrorism suspects is "going dark" as people increasingly communicate online instead of by telephone.

Essentially, officials want Congress to require all services that enable communications -- including encrypted e-mail transmitters such as BlackBerry, social networking websites such as Facebook and software that allows direct "peer-to-peer" messaging such as Skype -- to be technically capable of complying if served with a wiretap order. The mandate would include being able to intercept and unscramble encrypted messages.

The legislation, which the Obama administration plans to submit to Congress next year, raises fresh questions about how to balance security needs with protecting privacy and fostering technological innovation. And because security services around the world face the same problem, it could set an example that is copied globally.

James Dempsey, vice president of the Center for Democracy and Technology, an Internet policy group, said the proposal had "huge implications" and challenged "fundamental elements of the Internet revolution" -- including its decentralized design.

"They are really asking for the authority to redesign services that take advantage of the unique, and now pervasive, architecture of the Internet," he said. "They basically want to turn back the clock and make Internet services function the way that the telephone system used to function."

But law enforcement officials contend that imposing such a mandate is reasonable and necessary to prevent the erosion of their investigative powers.