A federal plan to deregulate high-speed Internet access might have an unintended consequence: The FBI is worried it could hamper the fight against terrorism.

The FBI and Justice Department are concerned that the Federal Communications Commission's decision to classify broadband as an "information" service could disrupt their ability to trace the e-mail and Internet activity of terrorists and other criminals.

Only "telecommunications" services are required by law to design their networks so that the government can easily tap into suspects' communications.

If phone company DSL and cable-modem providers read the law literally, authorities "may be hobbled in their ability to enforce the laws and protect national security," the FBI wrote to the FCC.

The agencies do not oppose the FCC proposal. They want the FCC to say that electronic-surveillance access rules also apply to the broadband information offerings of phone and cable companies.

The controversy centers on the collision of two ostensibly unrelated federal laws. Earlier this year, the FCC tentatively concluded that DSL and cable-modem services are information rather than telecommunications services, because they mainly entail storing and generating data rather than transmitting it.

As a result, analysts expect that the FCC will rule that they need not open their networks to rivals. Consumer advocates say that will drive up prices.

The Telecommunications Act currently forces the regional Bells to open their DSL networks to rivals; cable operators are under no such obligation.

The mandate on industry to design networks that can be wiretapped, however, is in the Communications Assistance for Law Enforcement Act (CALEA).

Such a design can cost several hundred million dollars. Without it, wiretaps are difficult, FBI officials say.

That law, however, applies only to telecommunications, not information services. The FBI argues, however, that it includes "joint-use" services, such as broadband, that have information and telecommunications pieces.

Critics of deregulation are skeptical. "They can't have their cake and eat it, too," says Jonathan Askin, general counsel for the Association for Local Telecommunications Services, which represent Bell rivals.

In other words, Askin believes that if the FCC upholds CALEA requirements with regard to wiretaps, at least on DSL companies, that could give open-access proponents such as his group ammunition for a possible court battle on its issue.

CALEA now applies to DSL, but not cable-modem service, FCC officials say. They would not comment on the FBI's petitions, which say CALEA covers both.

The United States Telecom Association, which represents Bells and other local phone monopolies, would not comment.

Verizon Communications, the largest Bell, believes its DSL still would be subject to CALEA, according to assistant general counsel John Goodman.