By John S. McClenahen The U.S. labor market could be moving from stable to softening. For the week ending Aug. 28, the number of initial claims for unemployment insurance rose to 362,000, some 19,000 more than the 343,000 recorded the previous week, the U.S. Labor Department reported on Sept. 2. The department's four-week moving average of initial claims also increased last week, to 343,000 from 336,750 the previous week. Merrill Lynch & Co., New York, notes that initial jobless claims are now at their highest level since April 10 -- and figures that the economic impact of Hurricane Charley accounts for only about 14,000 of the 29,000 total rise in initial claims during the past two weeks. " . . . That means the remaining increase of 15,000 is due to true economic fundamentals and suggests a softening in the labor market," says Merrill Lynch.