Although the television networks have written off Saturday as a day when few people -- particularly young people -- watch TV, viewers can often turn out in droves for specials and sports programming, it seems. For example, ABC's college football telecast of the Alabama-Virginia Tech game on Saturday averaged 6.60 million viewers, peaking in the final half hour at 10 30 p.m. with 7.69 million. All of the other networks offered reruns and did indeed fail to attract viewers. NBC averaged just 4.09 million for its schedule; CBS, 3.96 million; and Fox, 3.87 million.