Fox is understandably anxious over the much-anticipated return of “American Idol” on Monday, hoping the show will turn around what has been a dreadful season thus far salvaged only by strong baseball ratings.
   But there are no guarantees “Idol” can deliver Fox from the doldrums for a second straight season. In fact, history suggests that season three is when reality franchises start to fade.
   While the third season is expected to perform well, it may not be enough to push Fox to the same spectacular levels of last season, when the reality show carried the network to a May sweeps victory among adults 18-49.
  “I think it’s going to be pretty strong, but I don’t know if it will be at the same level as the past two seasons,” says Deana Myers, senior analyst at Kagan World Media. 
  “It’s hard to say, it’s hard to prejudge these things, but usually [a reality show] loses a little steam over time. It’s not as new, and people know the process.”
   Last year’s Wednesday “Idol” was the No. 2 show among 18-49s, averaging a 10.3 rating and 25 share over 18 episodes. Tuesday’s “Idol” averaged a 10.1/26, ranking No. 3 for the season.
   Viewership could dip by 15 percent or more versus last year, if past reality show monster hits can serve as a guide. 
  The finale of “Survivor: Africa” was more than 25 percent off from the preceding “Survivor: Australian Ouback” two years ago. Total average viewership for ABC’s “The Bachelor” dipped 27 percent from season two to season three.
   Of course, even a down “Idol” is way better than anything else airing on Fox right now. 
   Two 8.0 ratings per week could help perk up the third-place 18-49s network, especially without “Joe Millionaire” to lend an assist this year.
   “Typically, if you look back at the second arc of ‘Survivor’ and ‘The Bachelor,’ they did very strong compared to other arcs,” says Brad Adgate, senior vice president and corporate research director at Horizon Media.
   “I think this time around, I think it will be harder to replicate the buzz of the second installment of ‘American Idol.’”
   Fox has another reason for concern, too. 
   The troubling belly flop of “American Juniors” over the summer and relative disinterest in last month’s “World Idol” special seems to suggest that the 38 million people who watched the “Idol” finale last May are not the fanatics Fox had hoped.
   Myers says the “Juniors” flop happened so long ago that people may not even remember it. Then again, they also may need reminding about “Idol.” Because of baseball, Fox kept the start in January instead of moving it up.
   That’s probably the right move, because a Christmas layoff wouldn’t do much for ratings. With three new episodes airing Monday, Tuesday and Wednesday next week before the show settles into its usual Tuesday-Wednesday pattern, the show will now be hard to miss.
   “I do think they need to be careful,” Myers says. “Look what happened to ‘Who Wants to Be A Millionaire.’ That was a huge show, everyone was watching it, and then they got tired of it. I think that could easily happen to ‘American Idol.’ It’s the same type of program, and overexposure can hurt a show.”