One key to harnessing that wind lies at the end of a causeway jutting into the bay, on a mostly undeveloped island where eagles fish offshore and people walk in the quiet shade. Many officials see this spot, known as Sears Island, as the ideal site to build and launch a flotilla of turbines that could significantly lessen Maine’s reliance on fossil fuels. Standing in their way are environmental groups and local residents, all of whom are committed to a clean energy future and worried about the rapid warming of the earth. Still, they want the state to pick a different site for its so-called wind port, citing the tranquillity of Sears Island and its popularity and accessibility as a recreation destination.