KITTERY – The lawyer who represents the nation’s interests before the U.S. Supreme Court has sided with Maine in its border dispute with New Hampshire.

The two states are competing for ownership of the Portsmouth Naval Shipyard, located on an island in the middle of a river separating the two states.

New Hampshire contends the historic boundary rests along the low-water mark on the Maine shore; Maine argues the border cuts through the middle of the river. After years of disagreement, New Hampshire in March asked the court to settle the issue.

Maine since has asked to dismiss the case. That request was bolstered this week when Solicitor General Seth Waxman filed a friend-of-the-court brief making the same recommendation.

Waxman sided with Maine, saying that a decree signed by King George II in 1740 clearly established the boundary as the middle of the Piscataqua River and that a 1976 U.S. Supreme Court ruling reinforced that line.

The 1976 finding “precludes either state from now claiming that the King’s order does not provide the controlling law for establishing a continuation of their boundary landward” from the mouth of the harbor, Waxman said.

Shipyard workers who live in New Hampshire have been the driving force behind the dispute, arguing they should not have to pay Maine’s progressive income tax, which took effect in 1969. New Hampshire does not have a state income tax.

The solicitor general helps the attorney general in his or her duties and represents the interests of the United States before the Supreme Court. He decides whether the government will appeal cases and whether it will file friend-of-the-court briefs or intervene in any court.

Maine Assistant Attorney General Paul Stern was pleased with Waxman’s brief.

“The view of the solicitor general is highly regarded by the Supreme Court. From that perspective, this is good news from our standpoint,” he said.

New Hampshire Attorney General Philip McLaughlin disagreed with Waxman’s logic.

“The solicitor general is essentially saying this matter should be resolved procedurally based on the 1976 decision,” he said. “We’re saying it should be resolved on the merits of the evidence. The answer should be based not on what happened in 1976. It should answer the question, where is the shipyard?”

The court, which is scheduled to discuss the case Jan. 5, has several options.

It could grant the motion to dismiss – allowing Maine to continue to control the property – or could appoint a special master to further investigate the case. The court also could schedule oral arguments to clarify any unresolved issues.