KITTERY – The U.S. Supreme Court has set April 16 as the date for oral arguments on a motion to dismiss a long-standing dispute between Maine and New Hampshire over the location of the Portsmouth Naval Shipyard.

The shipyard is on an island in the middle of the Piscataqua River that separates the two states. At stake in the dispute is the $5 million in yearly income-tax revenue that Maine takes in from 1,300 New Hampshire residents who work at the yard.

The April hearing date means that the justices could rule by late June on Maine’s motion to dismiss the New Hampshire lawsuit.

“This is very exciting,” said Victor Bourre of Dover, N.H., a retired shipyard worker who has refused to pay the Maine tax while pushing his state to pursue the border battle. “I think it’s one of the final steps of the resolution of the border dispute,” he said.

The court could end the matter by dismissing the lawsuit, or it could reject Maine’s motion and send the dispute to a special master, leaving the dispute unresolved for years.

Maine considers its border to be in the middle of the river, which places the shipyard in Kittery. New Hampshire maintains that the boundary lies along the Maine bank, putting the yard on the Portsmouth, N.H., side. The issue was of little more than academic interest before Maine adopted a state income tax in 1969. New Hampshire, which has no income tax, revived the debate last spring by asking the high court to settle the issue once and for all.