By Edward Hoagland. HE heroes of many novels are dreamers.
Nature can be indifferent, too.
In Edward Hoagland's ''Seven Rivers West,'' the dreamer is Cecil Roop, the son of a former liniment company employee. LIKE any adventurer, Cecil is leaving one life to find another. Sutton was once party to the escape of a hippo in the Mississippi River. He's a platform diver, trained to survive a 40-foot jump into one foot of water. Sutton's circus spirit makes him a fit partner for a logger from Maine and Massachusetts who wants to capture and train grizzly bears.