WASHINGTON — An audacious plan to lay a multibillion-dollar wind power transmission spine under the seabed from southern Virginia to the New York City area will take a step forward on Tuesday with an announcement of plans for the first leg, a 189-mile segment running from Jersey City to a spot south of Atlantic City.

The proposed backbone, first outlined publicly in October 2010, is intended to link future wind farms far offshore, sparing them the expense and regulatory problems of bringing power lines all the way to shore individually, and to move power to land-based sources. The project’s backers, which include Google and other prominent investors, argue that the buried offshore spine, impervious to storms, could also come in handy in an emergency, providing a backup for hospitals and police stations and restarting power plants in blacked-out areas.

The latter selling point has gained importance for the line’s promoters as interest in offshore wind has suffered setbacks, including the declining price of natural gas, a competing energy source.

The Atlantic Wind Connection, the project’s sponsor, says the first segment would run from a substation called Cardiff, near Pomona, N.J., operated by Atlantic City Electric, out into the ocean 12 to 14 miles. That leg represents less than half of the 350-mile project, but the plan was always to build it in stages. Near the line’s southern end, it would tie into multiple wind farms in a region that the Obama administration has identified as prime territory for offshore wind.