WASHINGTON — The Federal Energy Regulatory Commission today approved a $700 million liquefied natural gas terminal proposed for Long Island Sound.

The terminal would be located 9 miles from Long Island and 10 miles from the Connecticut shoreline.

Environmentalists and many elected officials oppose the project, saying it could imperil the fragile ecosystem in Long Island Sound and that a terrorist attack on the facility could result in catastrophic results.

New York officials have yet to decide on issuing permits for the project. Connecticut officials have warned they will fight in court if the project is approved by federal regulators and New York.

Broadwater Energy, a consortium of Shell Oil and TransCanada Pipelines Ltd., wants to build the terminal, which would be 1,200 feet long and 82 feet high. Plans have called for construction to begin in October 2009 and for the terminal to be operating by December 2010.

FERC, which voted 5-0 to approve the project, says it will be the first floating terminal in America for storage and delivery of natural gas.

“It’s a reasonable and sensible decision by FERC,” a Broadwater spokesman, Gary Hale, said. “They have input from thousands of hours of efforts from the best scientific minds in the nation, environmentalists, and from the Coast Guard.”

Mr. Hale said the terminal is needed to meet region’s growing energy needs. The New York State Energy Plan, which projects a 37% growth in statewide natural gas use by 2021.

About half of the gas from the proposed terminal would go to New York City. Between 25% and 30% is targeted for Long Island, and the rest would go to Connecticut.

Governor Spitzer had planned to decide in April on whether the state should issue permits for the project. Governor Paterson has said he may postpone that decision.

Mr. Hale said he expects delays but is confident the terminal will be built.

“Some officials have talked about using Connecticut resources to go to court to appeal this, which I feel would be a waste of time and money, but I suspect that will happen,” he said.

Attorney General Richard Blumenthal of Connecticut said he plans to ask for an immediate rehearing and will take the state’s arguments to the U.S. Supreme Court if necessary.

He also urged Paterson to “drive a stake through this monster’s heart.”

“FERC’s decision to approve this environmental atrocity is ill-conceived, illogical and illegal,” General Blumenthal said. “FERC never met an energy project it didn’t like. This decision epitomizes the (Bush) administration’s lawless love for Big Energy projects, no matter how dangerous or destructive.”

The proposed Broadwater terminal would look like a ship and be moored to the bottom of the Sound by a tower embedded in the sea floor, allowing it to rotate in response to wind tide and current. It would be linked to the Iroquois gas pipeline.

In January, the staff of FERC concluded that the project would have no major environmental impact on the region.

The FERC staff report said potential harm to the environment from the project would be “largely limited” to the immediate vicinity of the terminal.

The report cited minimal to moderate problems that could result from the disturbance of the seabed during construction, air emissions from the vaporization of the liquefied gas, and threats of leaks from ship collisions, groundings, or even terrorism.

The report included 86 recommendations for mitigating potential problems, including the creation of a 5-mile safety and security zone around the terminal where commercial and recreational activity would be banned.