The Coast Guard icebreaker Polar Star, trapped by ice northwest of Alaska, planned to escape the Arctic by starting a voyage today through the disputed Northwest Passage with a Canadian escort, officials said. Canada’s decision to allow the U.S. vessel to sail the waterway accompanied by a Canadian Coast Guard icebreaker defuses a sensitive conflict between the neighbors. The Northwest Passage is a 1,000-mile stretch of water, frozen most of the year, between Canada’s mainland and its northern islands. The United States considers it an international waterway, but Canada claims ownership. The Polar Star got into trouble when it came to the rescue of two Canadian icebreakers, which called for help Sept. 28 when they became trapped in ice north of Alaska. The bigger Polar Star freed the Canadians, but was unable to crash through Chukchi Sea ice off northwest Alaska on its way to the Pacific. The Polar Star was faced with wintering over in the Arctic or taking a long detour through the Northwest Passage, down the Atlantic Coast, through the Panama Canal and back up the West Coast to Seattle.