ANCHORAGE, Alaska — In the quest for oil-free power, a handful of small companies are staking claims on the boundless energy of the rising and ebbing sea.

The technology that would draw energy from ocean tides to keep light bulbs and laptops aglow is largely untested, but several newly minted companies are reserving tracts of water from Alaska's Cook Inlet to Manhattan's East River in the belief that such sites could become profitable sources of electricity.

The trickle of interest began two years ago, said Celeste Miller, spokeswoman for the Federal Energy Regulatory Commission. The agency issues permits that give companies exclusive rights to study the tidal sites. Permit holders usually have first dibs on development licenses.

Tidal power proponents liken the technology to little wind turbines on steroids, turning like windmills in the current. Water's greater density means fewer and smaller turbines are needed to produce the same amount of electricity as wind turbines.

After more than two decades of experimenting, the technology has advanced enough to make business sense, said Carolyn Elefant, co-founder of the Ocean Renewable Energy Coalition, a marine energy lobbying group formed in May 2005.

In the past four years, the federal commission has approved nearly a dozen permits to study tidal sites. Applications for about 40 others, all filed in 2006, are under review. No one has applied for a development license, Miller said.

The site that is furthest along in testing lies in New York's East River, between the boroughs of Manhattan and Queens, where Verdant Power plans to install two underwater turbines this month as part of a small pilot project.

Power from the turbines will be routed to a supermarket and parking garage on nearby Roosevelt Island.

Verdant co-founder and President Trey Taylor said the six-year-old company will spend 18 months studying the effects on fish before putting in another four turbines.

The project will cost more than $10 million, including $2 million on fish monitoring equipment, Taylor said.

"It's important to spend this much initially," Taylor said. "It's like our flight at Kitty Hawk. It puts us on a path to commercialization, and we think eventually costs will fall really fast."

If all goes well, New York-based Verdant could have up to 300 turbines in the river by 2008, Taylor said. The turbines would produce as much as 10 mega-watts of power, or enough electricity for 8,000 homes, he said.

With 12,380 miles of coastline, the U.S. may seem like a wide-open frontier for the fledgling industry, but experts believe only a few will prove profitable. The ideal sites are close to a power grid and have large amounts of fast-moving water with enough room to build on the sea floor while staying clear of boat traffic.

"There are thousands of sites, but only a handful of really, really good ones," said Roger Bedard of the Electric Power Research Institute, a nonprofit organization in Palo Alto, Calif., that researches energy and the environment.

"If you're sitting on top of the best scallop fishing in the world, you can't put these things down there," said Chris Sauer, president of Ocean Renewable Power Co. in Miami. The two-year-old company is awaiting approval for federal study permits in Cook Inlet and Resurrection Bay in Alaska, and Cobscook Bay and the St. Croix River in Maine.

Other prime tidal energy sites lie beneath San Francisco's Golden Gate Bridge and in Knik Arm near Anchorage, Bedard said.

Government and the private sector in Europe, Canada and Asia have moved faster than their U.S. counterparts to support tidal energy research. As of June 2006, there were small facilities in Russia, Nova Scotia and China, as well as a 30-year-old plant in France, according to a report by EPRI.

"I expect the first real big tidal plant in North America is going to be built in Nova Scotia," said Bedard, who led the study. "They have the mother of all tidal passages up there."

The industry is coalescing over worries about dependence on foreign oil, volatile oil prices and global warming. Many states have passed laws requiring a certain percentage of energy from renewable sources, and tidal entrepreneurs believe they will be looking to diversify beyond wind and solar power.

Elefant said the industry is still trying to figure out how much energy it will be able to supply from tides, as well as waves.

"While ocean energy may not power everything in the U.S., it will be functioning in tandem with other renewable resources and supplement other sea-based technologies," said Elefant, a lawyer in Washington, D.C. "The most important thing is for the nation to invest in a diverse energy supply."