MOSCOW -- For centuries, mariners have dreamed of an Arctic shortcut that would allow them to speed trade between Asia and the West. Two German ships are poised to complete that transit for the first time, aided by the retreat of Arctic ice that scientists have linked to global warming.

The ships started their voyage in South Korea in late July and will begin the last leg of the trip this week, leaving a Siberian port for Rotterdam in the Netherlands carrying 3,500 tons of construction materials.

Russian ships have long moved goods along the country's sprawling Arctic coastline. And two tankers, one Finnish and the other Latvian, hauled fuel between Russian ports using the route, which is variously called the Northern Sea Route or the Northeast Passage.

But the Russians hope that the transit of the German ships will inaugurate the passage as a reliable shipping route, and that the combination of the melting ice and the shortcut's economic benefits -- trimming thousands of miles off various southerly routes -- will eventually make the Arctic passage a summer competitor with the Suez Canal.

"It is global warming that enables us to think about using that route," Verena Beckhusen, spokeswoman for the shipping company, the Beluga Group of Bremen, Germany, said in a phone interview.

University of Fairbanks (Alaska) geography professor Lawson W. Brigham, who led the writing of an international report on Arctic commerce, the Arctic Marine Shipping Assessment, confirmed that the passage of the two German ships appeared to be the first true commercial transit of the entire Northeast Passage from Asia to the West.

He credited Beluga for taking on both the summertime Arctic waters, which still pose threats despite the recent sea-ice retreats, and Russian red tape, a maze of permits and regulations. "This may be as much of a test run for the bureaucracy as for the ice," said Dr. Brigham, an oceanographer and former Coast Guard icebreaker captain.

But he also said it would be a long while before Arctic shipping routes take business from the Suez or Panama canals.

Company officials said the unloading in Siberia of 44 components for a Russian power plant should be completed bytomorrow, after which the ships will head to Rotterdam to deliver the rest of the cargo.

Sheets of pack ice still descend in hundred-mile-long tongues off the northern ice cap, and glaciers on the archipelagos off the coast shed icebergs that drift more dangerously in the otherwise ice-free summer seas. But the route is rarely wholly impassable these days, the Russian Transport Ministry said.

The pair of ice-hardened, 12,700-ton ships, the Beluga Fraternity and Beluga Foresight, were accompanied for most of the trip so far by one or two Russian nuclear icebreakers as a precaution, although they encountered only scattered small floes. At the most perilous leg of the journey, the passage around the northernmost tip of Siberia, the Vilkitsky Strait, ice covered about half the sea.