BANGOR – The oversight board of New England’s power grid believes a proposed high-volume transmission line for Bangor Hydro-Electric Co. will improve electricity reliability in the six New England states.

So it has concluded that all of New England’s 6.5 million ratepayers should share in the line’s construction costs.

The planned 345-kilovolt transmission line, which would run between Orrington and Keswick, New Brunswick, is expected to cost $90.4 million just from the Canadian border to Orrington.

On Thursday, the governing board, ISO-New England, agreed with Bangor Hydro that the transmission line plan, called the Northeast Reliability Interconnect, would add electricity reliability benefits to New England.

Those benefits include reducing overall electrical costs, making it more efficient to import and export power between Maine, New England and the Maritimes by reducing line losses, and providing additional supply during peak usage seasons, according to Rob Bennett, general manager of assets at Bangor Hydro.

“This is wonderful news for us,” said LuAnn Ballesteros, Bangor Hydro spokeswoman, about ISO’s approval of the cost-share plan.

What path the transmission line will follow is not known. Five routes are being evaluated, and Bangor Hydro will release the planned route in September. Then the utility will seek permits and regulatory approvals from municipalities, the Maine Public Utilities Commission and the Federal Energy Regulatory Commission.

“We’re hoping to have the line in service by the end of 2006,” Ballesteros said.