The Coast Guard late Thursday gave its coveted blessing, with conditions, to a proposal to build a liquefied natural gas offloading terminal in Mt. Hope Bay, removing a major stumbling block in a plan to bring LNG supertankers up Narragansett Bay and park them in the middle one of the state’s major waterways.

Local waterways are “suitable for the type and frequency of LNG marine traffic associated with this project,” Raymond J. Perry, captain of the Port of Southeastern New England, concluded.

It was the Coast Guard that essentially killed off an earlier incarnation of the plan by Weaver’s Cove Energy, ruling that the massive tankers would be unable to safely make the hairpin turns between bridges as they traveled up the Taunton River to unload the highly volatile fuel in Fall River.

Under Weaver’s Cove’s revised plan, the 145-foot-wide ships would dock in the middle of Mt. Hope Bay and pump their supercooled cargo, via 4.2 miles of insulated underground piping, through Somerset to a storage tank in Fall River, where the project is widely opposed.

“We’re pleased that the latest decision by the Coast Guard confirms that pursuing the offshore birthing option addresses the concerns that were the basis of the original denial,” Weaver’s Cove spokesman James A. Grasso said.

The ruling doesn’t mean that the project will ultimately be built. Grasso said 29 agencies must weigh in on the project.

The key decision will be made by Federal Energy Regulatory Commission, which is expected to hold hearings later this year. A ruling by FERC, which endorsed the first Weaver’s Cove proposal, typically takes a year or longer.

Grasso said the company is now on track to have the facility running in 2015.

“We’re disappointed in the Coast Guard decision and we disagree respectfully,” said Save The Bay spokesman John Torgan. “This just moves us into the next phase of the permitting process. We’re going to need to be more active in getting people engaged and fighting this.”

The focus now moves to the project’s environmental questions.

“This project will destroy 73 acres of winter flounder habitat through dredging and constructing the platform,” said Torgan. “We’ve been fighting for 30 years to improve the habitat and protect winter flounder” in Mt. Hope Bay.

The proposal calls for 70 supertanker trips into local waters each year, with each escorted by a security flotilla to protect against a terrorist attack, and requiring the temporary closing of the Claiborne Pell and Mt. Hope Bay bridges during the transits.

Rhode Island Senators Jack Reed and Sheldon Whitehouse, both Democrats, said the Coast Guard decision “fails to take the big picture into account [because] the scope of the proposed project and its attendant security measures will crowd out other water users to accommodate a single purpose and place a tremendous burden on taxpayers and local law enforcement.”

They vowed to fight the project, as did Attorney General Patrick C. Lynch, an expected candidate for governor, who called Tuesday’s recommendation misguided.

In his decision, Perry said the Weaver’s Cove plan must include security escorts for the supertankers, a safety and security zone for the ships while in transit and at berth, shoreline security, special aids to navigation, a training program for pilots and tug operations, an emergency response plan and a plan to reimburse agencies for the extra expenses the project will require.

gemery@projo.com