New mapping data could bolster any claims the U.S. might make in the Arctic as nations in the region compete for potentially rich reserves of oil, gas and minerals buried beneath the sea floor, federal scientists said Monday.

Federal officials said the data would support the U.S. should it choose to jockey with Russia, Canada and other circumpolar nations under the international Law of the Sea treaty to carve out boundaries off their northern coasts.

The Law of the Sea confers sovereign rights over a country's continental shelf beyond the normal boundary of 200 nautical miles if the country can substantiate its claims through scientific evidence.

Bathymetric soundings taken last year showed the foot of Alaska's continental slope extending more than 100 nautical miles farther from the U.S. coast than previously believed, according to the National Oceanic and Atmospheric Administration.

"We found evidence that the foot of the slope was much farther out than we thought," said Larry Mayer, the chief scientist for the expedition last year. "That was the big discovery."

The U.S. is the only Arctic nation not party to the Law of the Sea treaty, which is a contentious issue in Congress. The Bush administration has been pushing for its approval.

Scientists said their findings do not completely settle the question of where the U.S. could set a plausible boundary.

"There's no question that the potential U.S. continental shelf and the potential shelf from Canada will have some overlap," said Andy Armstrong, NOAA co-director of the Joint Hydrographic Center at the University of New Hampshire. "We'll have to work with bordering nations to sort out any potential overlaps."

Mayer said the boundary with Russia is "just about established."

The expedition, which cost at least $1.2 million, focused on a section of the Chukchi Sea 400 to 600 miles north of Alaska. Scientists covered more than 6,200 miles using multibeam sonar from the deck of an icebreaker, the U.S. Coast Guard cutter Healy, said Mayer, who is also co-director of the Joint Hydrographic Center at the university in Durham, N.H.

The resulting images of the relatively unexplored region are the most detailed ever collected and will be applied to a variety of research topics, said Capt. Steve Barnum director of NOAA's Office of Coast Survey.

"These are entirely new insights into what the ocean bottom looks like," Barnum said. "The data will be used to gain a better understanding of many things, including ecosystems and climate circulation models."

The next expedition is planned for mid-August through early September, Mayer said, and will follow a geologic feature that could extend the foot of the slope to the north and east.

A U.S. study suggests as much as 25 percent of the world's undiscovered oil and gas could be hidden beneath the Arctic seabed. Growing evidence that global warming is shrinking polar ice — opening up resource development and new shipping lanes — has added to the urgency of the claims.