An unarmed U.S. cruise missile parachuted to a soft landing on a frozen lake in northern Alberta, successfully completing a 1,500-mile test flight across the Canadian Arctic, officials said. The 3,000-pound missile was launched by a B-52 bomber over the Beaufort Sea in northern Canada and traveled at 500 m.p.h. at altitudes ranging between 1,000 and 4,000 feet over a zigzag course before landing four hours later. The test was the fourth cruise exercise in Canada in the last year. No further tests are planned for the rest of 1985, officials said.