AN FRANCISCO, April 9 — As cable, telephone and wireless companies compete to provide high-speed Internet access to homes, a new challenger is emerging based on a decidedly old technology.

The idea is to send Internet data over ordinary electric power lines. Proponents argue that it can be a competitive alternative to digital cable, telephone digital subscriber line and wireless efforts to connect the "last mile" between homes and Internet service providers.

Power-line networking has held out promise for several decades, in part because the electric grid is already in place, running to almost every residence in the nation, and also because it was thought that power companies would leap at the idea of a new revenue source — if the technology is proven.

But the idea has elicited deep skepticism from technologists who argue that the electric power network is a remarkably difficult environment for transmitting digital information. Moreover the nation's electric power industry has for the most part remained complacent about the technology.

Still, the technology is getting sudden attention in response to several trial efforts around the country and in other nations. Today, Michael K. Powell, the chairman of the Federal Communications Commission, gave the concept a further boost when he toured a demonstration site for the technology in Potomac, Md.

The agency and its chairman have said they are backing the power-line approach in an effort to stir competition and offer greater consumer choice.

"I was struck by how it has matured," Mr. Powell said. He said the F.C.C. was preparing to undertake a regulatory proceeding that could help pave the way for commercial deployment. "I'm optimistic," he said.

The F.C.C. has licensed seven companies to conduct field tests in roughly a dozen communities around the country, including Raleigh, N.C.; Potomac, Md.; Cincinnati,; Lehigh, Pa.; and Briarcliff, N.Y.

But even if the technology can be made to work, weighty business questions remain. What is unclear, according to analysts and academics who follow the emerging industry, is whether any of the fledgling competitors can make money offering consumers lower-cost access to high-speed data, including Internet-based telephone calls and video.

The technology requires the installation of equipment that acts as a switch to transfer data between the power lines and fiber optic lines, which traditionally carry Internet traffic.

Currently there are several competing approaches. Some companies are developing the technology to transmit data over traditional fiber cables until it reaches telephone poles that serve small clusters of homes, where it would then be transferred to the power lines. Others are taking a more radical approach, trying to transmit Internet data directly from electrical power substations that serve several hundred homes and businesses in a neighborhood.

For the more ambitious plans, "there are all sorts of costs associated with installation," said Rahul Tongia, a researcher at Carnegie Mellon University in Pittsburgh. "The costs do involve people going up the poles. That's not to say these costs are crippling, but they have to be factored in."

At least one company is trying to minimize the costs associated with home installation by relying on inexpensive consumer equipment that is already available to use electrical wiring as a local area network within the home.

"What we are now seeing in our customer's homes," said Jay Birnbaum, president of Current Technologies, "are data rates ranging from two to four megabits," which is much faster than old-fashioned dial- up services but not particularly fast for high-speed broadband services. Current Technologies, based in Germantown, Md., is conducting the Potomac trial that Mr. Powell visited today, in cooperation with the local power provider, the Potomac Electric Power Company.

Despite the obstacles, some power companies may forge ahead because of further advantages from providing the service, including the ability to regulate the flow of electricity more directly and to use the network to check power meters over the Internet rather than visiting individual homes.

PowerWan, a start-up in Palo Alto, Calif., has begun testing a technology capable of doing just that in a handful of homes in Hawaii. Moreover, the company says it can offer data rates at twice the speed of telephone line D.S.L., said John Wheadon, PowerWan's acting chief executive.