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 like BlackBerry, social networking websites like Facebook and software that allows direct “peer to peer” messaging like 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 lawmakers 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.

“We’re talking about lawfully authorized intercepts,” said Valerie Caproni, general counsel for the FBI. “We’re not talking expanding authority. We’re talking about preserving our ability to execute our existing authority in order to protect the public safety and national security.”

Investigators have been concerned for years that changing communications technology could damage their ability to conduct surveillance. In recent months, officials from the FBI, the Justice Department, the National Security Agency, the White House and other agencies have been meeting to develop a proposed solution.

There is not yet agreement on important elements, like how to word statutory language defining who counts as a communications service provider, according to several officials familiar with the deliberations.

But they want it to apply broadly, including to companies that operate from servers abroad, like Research In Motion, the Canadian maker of BlackBerry devices. In recent months, that company has come into conflict with the governments of Dubai and India over their inability to conduct surveillance of messages sent via its encrypted service.

In the United States, phone and broadband networks already are required to have interception capabilities, under a 1994 law called the Communications Assistance to Law Enforcement Act. It aimed to ensure that government surveillance abilities would remain intact during the evolution from a copper-wire phone system to digital networks and cell phones.

Often, investigators can intercept communications at a switch operated by the network company. But sometimes — like when the target uses a service that encrypts messages between his computer and its servers — they must instead serve the order on a service provider to get unscrambled versions.

Like phone companies, communication service providers are subject to wiretap orders. But the 1994 law does not apply to them. While some maintain interception capacities, others wait until they are served with orders to try to develop them.

The FBI’s operational technologies division spent $9.75 million last year helping communication companies — including some subject to the 1994 law that had difficulties — do so. And its 2010 budget included $9 million for a “Going Dark Program” to bolster its electronic surveillance capabilities.

Beyond such costs, Caproni said, FBI efforts to help retrofit services have a major shortcoming: The process can delay their ability to wiretap a suspect for months.

Some services encrypt messages between users, so that even the provider cannot unscramble them.

There is no public data about how often court-approved surveillance is frustrated because of a service’s technical design.

But as an example, one official said, an investigation into a drug cartel earlier this year was stymied because smugglers used peer-to-peer software, which is difficult to intercept because it is not routed through a central hub. Agents installed surveillance equipment in a suspect’s office, but that tactic was “risky,” the official said, and the delay “prevented the interception of pertinent communications.”

According to several other officials, after the failed Times Square bombing in May, investigators discovered that the suspect, Faisal Shahzad, had been communicating with a service that lacked prebuilt interception capacity. If he had aroused suspicion beforehand, there would have been a delay before he could have been wiretapped.

To counter such problems, officials are coalescing around several of the proposal’s likely requirements:

Communications services that encrypt messages must have a way to unscramble them.

Foreign-based providers that do business inside the United States must install a domestic office capable of performing intercepts.

Developers of software that enables peer-to-peer communication must redesign their service to allow interception.