What was once the most anticipated new show of the season left the air with a whimper last night for an extended and perhaps permanent hiatus.

“Studio 60 on the Sunset Strip” fell to a series-low 2.6 adults 18-49 rating, according to Nielsen overnights, finishing 0.1 behind ABC’s struggling “What About Brian” in the 10 p.m. timeslot.

That was 0.2 behind its 2.8 overnight last week, its previous season low. And it was 24 percent below “Strip’s” 3.4 season-to-date average. The recent ratings decline has come as the drama about life at a “Saturday Night Live”-style late-night show changed its focus from Hollywood insider stuff to romance.

Next week NBC is replacing “Strip” with midseason drama “The Black Donnellys.” The network originally had planned to begin airing “Donnellys” on March 5, allowing “Strip” to finish out the February sweeps in the valuable post-“Heroes” timeslot.

But after “Strip” continued to slide in recent weeks, NBC decided to move “Donnellys” in before “Heroes” moved to repeats.

Whether “Strip” will return at all now seems questionable. NBC has not announced a return date for the program, saying only that it will be back later this season.

Unless “Donnellys” really bombs, “Strip” won’t resurface on Monday. The network has a powerful lineup in the 8-10 p.m. slots, yet “Strip” is now losing more than half its lead-in and pulling the longtime No. 1 network on Mondays down to second or third.

At the least, it seems a sure bet that “Strip,” which was created by “West Wing’s” Aaron Sorkin and boasted an A-list, expensive cast, will not be back next year.

Indeed, last night CBS finished first among 18-49s with a 4.8 average rating and a 12 share. It was followed closely by NBC at 4.5/11 and Fox at 4.4/11, with ABC fourth at 3.3/8, Univision fifth at 1.7/4 and CW sixth at 1.1/3.
 
NBC started the night on top with a 4.8 rating at 8 p.m. for “Deal or No Deal.” Fox was second with a 3.9 for “Prison Break,” ABC third with a 3.7 for “Wife Swap,” tying last week’s season high, and CBS fourth with a 3.4 average for “How I Met Your Mother” (3.5) and “The Class” (3.3). Univision was fifth with a 2.3 for “La Fea Mas Bella” and CW sixth with a 1.2 average for “Everybody Hates Chris” (1.3) and “All of Us” (1.1).
 
NBC led again during a competitive 9 p.m. hour with a 6.0 for “Heroes.” CBS was second with a 5.1 average for “Two and a Half Men” (5.3) and “Rules of Engagement” (4.9), Fox third with a 5.0 for “24” and ABC fourth with a 3.5 for “Supernanny.” Univision was fifth that hour with a 1.6 for “Mundo de Fieras” and CW sixth with a 1.0 average for “Girlfriends” (1.0) and “The Game” (1.0).
 
CBS took the lead at 10 p.m. with a 5.9 for “CSI: Miami,” followed by a 2.7 for ABC for “What About Brian.” NBC dropped to third with a 2.6 for “Strip” and Univision was fourth with a 1.2 for “Cristina.”
 
Among households, CBS led the night with a 9.2 average rating and a 14 share. NBC was second at 7.7/12, Fox third at 6.9/10, ABC fourth at 5.3/8, Univision fifth at 2.2/3 and CW sixth at 1.7/2.