Clifford Krauss reported from Canada for this article, Steven Lee Myers from Russia, Andrew C. Revkin from New Hampshire and Washington, and Simon Romero from Norway. Craig Duff contributed reporting from Canada, Norway, Russia and Alaska.

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It seems harsh to say that bad news for polar bears is good for Pat Broe. Broe, a Denver entrepreneur, is no more to blame than anyone else for a meltdown at the top of the world that threatens Arctic mammals and ancient traditions and lends credibility to dark visions of global warming.

Still, the newest study of the Arctic ice cap finding that it faded this summer to its smallest size ever recorded is beginning to make Broe look like a visionary for buying this derelict Hudson Bay port facility from the Canadian government in 1997. Especially at the price he paid: about $7

By Broe's calculations, Churchill could bring in as much as $100 million a year as a port on Arctic shipping lanes that are shorter by thousands of miles than routes to the south, and traffic would only increase as the retreat of ice in the region clears the way for a longer shipping season.

The Arctic is undergoing nothing less than a great rush for virgin territory and natural resources worth hundreds of billions of dollars.

Even before the polar ice began shrinking more each summer, countries were pushing into the Barents Sea, lured by undersea fields of oil and natural gas and emboldened by advances in technology. But now, as thinning ice simplifies construction of drilling rigs, exploration is likely to move even farther north.

Last year, scientists found hints of oil in seabed samples just 200 miles, or 320 kilometers, from the North Pole.

A quarter of all undiscovered oil and natural gas lies in the Arctic, the U.S. Geological Survey estimates.

The polar thaw is also starting to unlock other treasures: lucrative shipping routes, perhaps even the storied Northwest Passage; new destinations for cruise ships; and important commercial fisheries.

"It's the positive side of global warming, if there is a positive side," said Ron Lemieux, transportation minister of Manitoba, which is investing millions in Churchill.

If the melting cascades, as many Arctic experts expect, the mass of floating ice that has crowned the planet for millions of years may largely disappear for entire summers this century. Instead of the white wilderness that killed explorers and defeated navigators for centuries, the world would have a blue pole on top, a seasonally open sea nearly five times the size of the Mediterranean.

But it is not clear how to divide up that area. Under the UN Convention on the Law of the Sea, territory is determined by how far a country's continental shelf extends into the sea, spurring governments to map the sea floor and make claims.

In 2001, Russia made the first move, staking out virtually half of the Arctic Ocean, including the North Pole. Moscow sought to bolster its claim by sending a research ship north to gather geographical data. On Aug. 29, it reached the pole without the help of an icebreaker the first surface ship ever to do so.

The United States, an Arctic country itself because of Alaska, could also try to expand its territory. But several senators who oppose any possible infringement on U.S. sovereignty have repeatedly blocked ratification of the UN treaty.

A look at a globe from above explains why a new frontier matters. Countries that one might think of as being half a world part instead are, relatively speaking, startlingly close neighbors.

Increasingly, big corporations, the eight countries with Arctic footholds and other nations farther south are betting on the possibility of a great transformation.

GO NORTH

To understand the practical terms of this new rush for territory, opportunity and resources, a good place to begin is Hammerfest, Norway, one of the northernmost towns in the world.

Hammerfest is starting to swell with young people from other parts of Norway and Finland, Russia and Asia, as well as with highly trained technical workers from Europe and North America. They are drawn by Snohvit, a mammoth complex being built to receive natural gas piped from the Barents Sea and liquefy it for shipping.

The government, which controls the complex in part through its majority ownership of the company Statoil, wants Snohvit to put Norway in the forefront of Arctic energy exploration. Being first, however, has had its challenges in the severe operating environment of the High North, as Arctic areas are called in Norway. Huge cost overruns have put the project's price tag at $8.8 billion, almost 50 percent above its original estimate.

The project has a firm backer in John Doyle Ong, the U.S. ambassador in Oslo. Snohvit is scheduled to start sending liquefied natural gas to the Cove Point port in Maryland in 2007, just as American imports of liquefied gas from competing sources in the Middle East and Africa are set to rise rapidly. Importing natural gas from a stable country like Norway the third-largest oil exporter after Saudi Arabia and Russia is a rare option these days.

While natural gas is certainly valued, the prize generating the biggest interest is oil. Virtually every large international energy company is studying how eventually to win permission from Norway and Russia to explore in the Barents, and the Norwegian Polar Institute has been contacted repeatedly by oil companies to explore the feasibility of drilling in the icier waters north of Spitsbergen.

Jan-Gunnar Winther, director of the institute, said the seasonal melting of the polar cap might allow access to more petroleum deposits but also create more challenges. "A warmer climate in the north would mean more icebergs, rather than less," he said. "There will be obstacles in getting to the petroleum, but if oil prices stay high there will be enticements as well."

NEW FRONTIERS

"Stalin once just drew a line from Murmansk to the North Pole and then to Chukchi and said, 'U.S.S.R. Polar Region' and nobody worried about it," said Artur Chilingarov, an Arctic explorer and deputy speaker of Russia's lower house of Parliament. Now the lines will be drawn by an international commission and the geography of the seabed itself.

That means that the Arctic land grab could be decided in part inside a lab at the University of New Hampshire in Durham. At the Center for Coastal and Ocean Mapping there, scientists study sonar scans of the seabed from a 2002 expedition on a U.S. Coast Guard icebreaker in waters north of Barrow, Alaska.

With only fragments of the Arctic surveyed so far, by icebreaker or submarine, countries are mounting mapping expeditions to claim the most territory they can.

The exclusive economic zone controlled by a country generally extends 230 miles from its shores. But under Article 76, in the Law of the Sea, that zone can expand if a nation can convince other parties to the treaty that there is a "natural prolongation" of its continental shelf beyond that limit.

The shelf is the relatively shallow extension of a landmass to the point where the bottom drops into the oceanic abyss. But in many places, the drop-off is a gentle slope or is connected to long- submerged ridges that, if precisely mapped, might add thousands of square miles to a country's exploitable seabed.

Claims of expanded territory are being pursued the world over, but the Arctic Ocean is where experts foresee the most conflict. There the boundaries of five nations o Russia, Canada, Denmark, Norway and the United States converge, the way sections of an orange meet at the stem. (The three other Arctic nations, Iceland, Sweden and Finland, do not have coasts on the ocean.)

Under the Law of the Sea, countries that ratified the treaty before May 13, 1999, have until May 13, 2009, to make claims. Other countries have 10 years from their date of ratification.

Territorial disputes ultimately imply questions about a countryis ability to de$-$fend its interests. In the Arctic, Canada has acted aggressively to ensure sovereignty over a domain it long neglected.

Already, oil tanker traffic is rising and fishing boats are going farther north. The Royal Canadian Mounted Police is concerned that melting seaways could make it easier for narcotics traffickers to reach indigenous communities, and for organized crime to exploit the growing diamond trade.

Canada's aim is not only to tighten control of its territory, but also to establish a strong posture in future negotiations over the Northwest Passage, the long-sought shortcut from Europe to Asia across the top of Canada. Murmansk, on the Russian Arctic coast, and Churchill are unlikely sister cities. Churchill is not a city at all, but a barren outpost of 1,100 people on the western shore of Hudson Bay. It survives on the 15,000 tourists who visit each year for the chance to see and photograph migrating polar bears. Murmansk, by contrast, has a population of 325,000, making it the biggest city inside the Arctic Circle.

Though it lies north of Churchill, which is ice-bound eight months a year, Murmanskis harbor is ice-free, the ideal base for the Russian Arctic fleet and commercial shipping. One thing the communities have in common, however, is hard times. Churchill, never much to begin with, lost most of its population when Canada finished phasing out the Fort Churchill military base in the 1980s. Murmansk, like the rest of Russia, lost economic ground with the collapse of the Soviet Union. But the more relevant connection is an accident of geography and a shared dream: that the thawing of the Arctic Ocean would help create the so-called Arctic Bridge, a shipping route with their ports as the logical terminals The advantage of maritime shortcuts across the top of the world can be startling.

For example, shipments from Murmansk to midcontinental North America by the well- worn route through the St. Lawrence Seaway and Great Lakes to Thunder Bay, in western Ontario, typically take 17 days. The voyage from Murmansk to Churchill is only eight days under good conditions, and from Churchill, rail links snake down through Manitoba, the American Midwest and points south all the way to Monterrey, Mexico.

For Murmansk, an extended shipping season in Arctic ports that are now frozen much of the year could mean a boon in traffic o to the west and, perhaps once again, to the East Asia.

The same way an Arctic Bridge could drastically cut the distance to Canada, a revived Northern Sea Route could shorten the journey for goods and raw materials from Northeast Asia to Europe by 40 percent.