One of the big questions for Fox heading into the fall is how its sophomore hit “House” will perform without “American Idol” as a ratings-pumping lead-in. If summer reruns are any indication, the medical drama should be just fine.
   An 8 p.m. episode of the show last night averaged a 2.2 overnight rating among viewers 18-49, a slight increase over the 2.0 rating the show averaged at 8 p.m. the previous two Tuesdays.
   A 2.2 doesn’t sound great, but for a summer repeat it’s decent. Consider that ABC’s “Desperate Housewives,” last season’s highest-rated drama in 18-49s, has barely averaged a 2.0 the past few weeks, while NBC’s big freshman hit “Medium” managed just a 1.8 Monday night.
   “House” has averaged a 2.4 18-49 rating for six episodes aired since Aug. 3, though four of those episodes were in the 9 p.m. timeslot that “Prison Break” occupied last night.
   The show has consistently finished second in its timeslot opposite CBS’s mild summer hit “Big Brother.” And it’s ranked in the top 15 for most of the summer. 
   That has to be a relief for Fox, which plans to use “House” to help launch new drama “Bones” next week. It needs the show, which features Emmy nominee Hugh Laurie, to perform well this fall to keep the network in decent position for when “Idol” returns in the winter.
   “House” finished tied for second in its timeslot last night with a Hurricane Katrina-focused episode of CBS’s “48 Hours,” both finishing 0.1 behind NBC’s “Dateline.”
   With the help of “Big Brother,” the night’s highest-rated show among 18-49s, CBS led the night with a 2.9 average rating and an 8 share. Fox was second at 2.3/7, NBC third at 2.2/6, ABC fourth at 2.0/5, the WB fifth at 1.3/4 and UPN sixth at 1.1/3.
   At 8 p.m. NBC led with “Dateline,” followed by “House” and “48 Hours.” ABC was third that hour with a 2.0 average for repeats of the comedies “According to Jim” (2.0) and “Rodney” (1.9).
   CBS took the lead at 9 p.m. with a 3.4 average for “Big Brother.” Fox was second with a 2.5 for “Prison Break” and ABC third with a 2.4 for another hour of “Jim” (2.3) and “Rodney” (2.4) repeats.
   At 10 p.m. CBS led again, this time with a 3.1 average rating for “Rock Star: INXS,” NBC was second with a 2.7 for a repeat of “Law & Order: Special Victims Unit” and ABC third with a 1.6 for a “Boston Legal” rerun.
   Among households, CBS led the night with a 5.2 average rating and an 8 share. NBC finished second at 4.6/7, Fox third at 4.2/7, ABC fourth at 3.9/6, the WB fifth at 2.1/3 and UPN sixth at 1.7/3.