TONIGHT'S MUST-SEE

"30 Rock," 8:30 and 9:30 p.m., NBC. With its offbeat wit, this show should have a big audience. Instead, it's been wobbling. It goes on the shelf next week, making room for a lesser show, "Andy Barker, P.I." So let's catch these episodes while we can. Both center on Liz (Tina Fey, the show's creator), who runs a sketch-comedy show. In the first episode, the network guy (Alec Baldwin) gives his foundering brother (Nathan Lane) a job with the show. In the second, a rerun, Jenna (Jane Krakowski) is furious. Tracy (Tracy Morgan) has his name in the title of her show; he's also been given her guest slot on Conan O'Brien's show. Things get worse when his prescription drugs combine. Some moments are wildly funny.

"The Office," 7:30 and 9 p.m., NBC. The first rerun has the offices merging. Jim is near Pam again but has a new girlfriend. The second is a drolly clever one written by Ricky Gervais and Stephen Merchant, who created the original, British "Office." Word spreads that one of the employees is an ex-convict.

OF NOTE

"American Idol," 7 p.m., Fox. Four people will be trimmed tonight and the show will have its 12 finalists. After that, it can settle back into its Tuesday-Wednesday mode, with one singer cut each week.

"Ugly Betty," 7 p.m., ABC. This reruns the second episode in which Salma Hayek (who also produces the show) plays the gorgeous Sofia. Daniel is enamored, but she and her entourage are misbehaving.

"My Name is Earl," 7 p.m., NBC. Earl must make amends for once throwing an old guy out of his rock band — and for sleeping with the mother of his band mate, Ralph (Giovanni Ribisi).

"CSI: Crime Scene Investigation," 8 p.m., CBS. Two boys are missing in a neighborhood that includes a pedophile.

"Are You Smarter than a Fifth Grader," 8 p.m., Fox. After three runs last week, this fun quiz show has settled into a weekly hour.

"Scrubs," 8 p.m., NBC. A soldier is depressed after learning he can't return to fighting.

"Grey's Anatomy," 8 p.m., ABC. In a rerun, George's father is in the hospital needing heart surgery. Meredith is helping a girl who seems more attached to her nanny than to her mother.

"Shark," 9 p.m., CBS. Stark wants to prosecute an arms broker. However, the FBI presents complications.

"Men in Trees," 9 p.m., ABC. Marin goes through two harsh experiences — an earthquake and the local beauty salon.