BY LINDA BENSON rom budding adolescents to the college-bound, the newest additions to teenage fashion story this fall is long, neat, narrow — and knit. The fall, 1986 version is most often 100% cotton knit, and bears a striking resemblance to the tried-and-true sweat suiting material or morning jogging and exercising routines. But here is where the similarity ends. The new cotton knit is thinner in weight, often ribbed, or carefully worked with intricate details on 177collars and cuffs. And of course, shoulder pads under everything! Whether in tops, narrow skirts or calf-hugging pants, this fabric has become as important and as versatile on the young fashion scene as denim. So far, there doesn't seem to be any threat to the popularity of that all-American blue-jeaned Continued on Page 12 The layered look: a khaki top over matching skirt. Brown scarf is draped over a shoulder and tucked into a leather and silver Moroccan belt. Photographs by June Chaplin.