PORTLAND (AP) – An energy consortium with Maine ties was chosen to build a $300 million undersea electric transmission line that’s the first link in a 2,000-mile network that could some day connect New York City with Maine and the Canadian Maritimes.

The Long Island Power Authority announced Wednesday that it had picked the Neptune Regional Transmission System to do the job. Neptune is partly owned by Cianbro Corp. of Pittsfield, the state’s largest construction company.

Cianbro owns a 30-percent stake in Atlantic Energy Partners LLC, which owns the Neptune project. Other stakeholders include a subsidiary of Curtis, Thaxter, Stevens, the Portland law firm. Other partners are in Connecticut, Massachusetts and Canada.

Neptune has been working for three years to advance its vision of a network of cables, buried in the mud under the Gulf of Maine, plugged into power plants in Nova Scotia, New Brunswick and Maine, and hooked up to Boston and New York City.

Flowing through the $3 billion system would be a total electric capacity of 4,800 megawatts, the equivalent of six large power plants, or roughly enough energy for 5 million homes.

Running transmission lines under the ocean would sidestep opposition that often arises over plans to build new power plants near the cities, or to string new transmission corridors through suburbs and forests.

“We’re confident that over time this will be a solution for Maine to import and export energy,” said Peter Vigue, Cianbro’s president.

The line being built for the Long Island Power Authority would be the first phase of what’s being billed as the world’s largest undersea power network, in terms of the number of connections and miles of cable. The entire project would take several years to complete and be built in four phases.

The idea is to generate cheaper power in rural areas and ship it to high-demand areas. Electricity costs more in the urban Northeast and supplies are tight, especially in summer.

Maine is a net exporter of electricity.

But the overhead transmission lines that currently connect Maine with New Hampshire and southern New England are at capacity, limiting the amount of power they can handle at times of peak demand.