The cancellation clock may well be ticking on ABC’s Tuesday comedies, “Big Day” and “Help Me Help You.”

The two shows dipped to series lows last night, combining for just a 1.6 adults 18-49 rating in the 9 p.m. timeslot, according to Nielsen overnights. That was down 20 percent from last week, when they averaged a 2.0. And it was down 30 percent from a 2.3 the week before, when “Day” premiered.

“Day” averaged a 1.8, down a full point from its premiere. Meanwhile, “Help,” which got a boost in its first weeks airing as the lead-out to megahit “Dancing with the Stars,” has really suffered since “Stars” left the air.

The well-reviewed Ted Danson comedy averaged a 1.4 last night, half of its season-to-date 2.8 average in 18-49s.

The two shows combined to average just 4.2 million total viewers in the timeslot, losing more than half their lead-in of 11 million from “Dr. Seuss’ The Grinch Who Stole Christmas.”

That tiny lead-in pulled down ABC’s 10 p.m. lead-out “Barbara Walters Presents: The 10 Most Fascinating People of 2006,” which was down 24 percent from last year to a 3.1.

The network surely won’t want to keep the sinking sitcoms on too much longer, not when it’s eyeing first place for the season among adults 18-49. Though it has a big lead on Fox, the latter is expected to catch up when “American Idol” returns next month.

“House”-led Fox was first for the night among viewers 18-49 with a 4.2 average rating and an 11 share. CBS was second at 3.7/10, ABC third at 2.9/8, NBC fourth at 2.4/7, Univision fifth at 1.6/4 and CW sixth at 0.7/2.
 
CBS led off the night on top, posting a season-best 4.3 rating at 8 p.m. for “NCIS.” ABC was second with a 3.9 for the animated “How the Grinch Stole Christmas,” NBC third with a 2.3 for “Friday Night Lights” and Univision fourth with a 2.2 for “La Fea Mas Bella.” Fox was fifth that hour with a 1.9 for “Standoff” and CW sixth with a 0.9 for a repeat of “Gilmore Girls.”
 
Fox jumped into the lead at 9 p.m. with a 6.5 for “House,” followed by CBS with a 3.7 for “The Unit.” That put NBC third with a 2.1 for a repeat of “Law & Order: Criminal Intent,” ABC fourth with a 1.6 average for “Day” (1.8) and “Help” (1.4), Univision fifth with a 1.5 for “Mundo de Fieras” and CW sixth with a 0.6 for the “Family Friendly Awards.”
 
At 10 p.m. ABC was on top with a 3.1 for “Fascinating.” CBS was second with a 3.0 for a repeat of “Criminal Minds,” NBC third with a “Law & Order: Special Victims Unit” rerun and Univision fourth with a 1.2 for “Ver Para Creer.”
 
CBS finished first for the night among households with an 8.7 average rating and a 14 share. Fox was second at 6.5/10, NBC and ABC tied for third at 5.1/8, Univision fifth at 2.1/3 and CW sixth at 1.5/2.