As the fashion world clings to the sleek and sexy or the bold and graphic looks that have made lariats, hoops, and sensual drop earrings so popular, clothing designers and jewelry designers are on the lookout for the next big trend. And that, say fashion forecasters, is likely to be a reincarnation of a past big trend. Perhaps the economically uncertain times have inspired a longing for the comfort of an earlier era, or maybe fashion is searching for something it hasn't revisited recently, but for 2002, the hottest ideas are at least 100 years old. Among the up-and-coming looks is one that echoes Little House on the Prairie. Following on the country or equestrian look that dominates fall and winter fashion, the prairie style features puffy sleeves, full skirts, high collars, and shearling accessories and is a favorite of designers like Mark Jacobs. Ruffles and buttons are common accent