Whether the Knoxville World's Fair will reach its target of 11 million paying visitors is a subject of intense interest here. Knoxville newspapers print daily and cumulative attendance totals as well as front-page graphs showing the pace at which every millionth visitor was recorded. That pace has slowed dramatically since attendance peaked in late June. Not quite 9 million people have pushed through the turnstiles since the fair opened May 1. Such factors as the return of University of Tennessee students this week, an attractive UT home football schedule, and the arrival of fall foliage season in this scenic mountainous region are expected to help increase the number of visitors by the Oct. 31 closing. Fair officials remain optimistic that the target will be reached, but concede that work schedules for many employees have been cut because of the sagging visitor count.