WASHINGTON  Google and a New York financial firm have each agreed to invest heavily in a proposed $5 billion transmission backbone for future offshore wind farms along the Atlantic Seaboard that could ultimately transform the region’s electrical map.

The 350-mile underwater spine, which could remove some critical obstacles to wind power development, has stirred excitement among investors, government officials and environmentalists who have been briefed on it.

Google and Good Energies, an investment firm specializing in renewable energy, have each agreed to take 37.5 percent of the equity portion of the project. They are likely to bring in additional investors, which would reduce their stakes.

If they hold on to their stakes, that would come to an initial investment of about $200 million apiece in the first phase of construction alone, said Robert L. Mitchell, the chief executive of Trans-Elect, the Maryland-based transmission-line company that proposed the venture.