WASHINGTON — The Supreme Court sounded skeptical Monday of the National Park Service's authority to prevent an Alaskan moose hunter from using his motorized rubber boat to access remote areas of the state.

The justices heard arguments in a case that tests the limits of the federal government's authority in a state in which more than 60 percent of the land is federally owned.

The state and moose hunter John Sturgeon are arguing that the Park Service cannot enforce a national ban on amphibious vehicles known as hovercraft on a river in Alaska for which the state claims ownership, even though it runs through a national conservation area.

Sturgeon won an earlier round at the Supreme Court.

The case stems from Sturgeon's 2007 encounter with three park rangers who ordered him off the Nation River within the Yukon-Charley Rivers National Preserve in northeast Alaska. The rangers told him it was illegal to operate the noisy craft that can navigate shallow water or even mud. He sued in 2011.

The issue is whether a federal law enacted in 1980 to protect undisturbed land but also allow Alaska residents to maintain their way of life provides an exception to Park Service regulation of rivers that pass through national parks.

"Well, but, I mean, the waters are very important to Alaskans' way of life in the way they aren't elsewhere," Chief Justice John Roberts said, voicing doubt about the Trump administration's reading of the law that gives the federal government sweeping control of the waterways.

Justice Department lawyer Edwin Kneedler told the court that the 1980 law is a compromise because it allows hunting and airplane use in areas that usually are closed to those activities in national parks in other states.

But Congress did not intend to allow hovercraft to be used, Kneedler said, calling them very loud and unsightly.

Roberts didn't sound persuaded by that argument. "While you may think a hovercraft is unsightly, I mean, if you're trying to get from point A to point B, it's pretty beautiful," he said.

That comment aligned with the argument made by Alaska assistant attorney general Ruth Botstein, who said the law protected the state's control over rivers. "Our rivers are our only roads," Botstein said.

The session Monday also displayed the difficulty the justices were having in reconciling the precise language of the 1980 law with arguments on both sides.

"I've burned up an awful lot of gray cells trying to put together the pieces of this statute," said Justice Samuel Alito.