Headlining a new sitcom after appearing as a supporting player in the phenomenally successful "Cheers" would be hard enough. But imagine being the second supporting player from "Cheers" to headline a new sitcom, with the added pressure that the guy who blazed the trail before you, Kelsey Grammer of "Frasier," wound up in the most creatively successful sitcom spinoff in TV history. That's the dilemma facing George Wendt tonight as he launches his own CBS sitcom -- one in which, to make it even tougher, he's not playing Norm.
* "The Cosby Mysteries" (8 p.m.-9 p.m., Channel 11) -- Mr. Wendt isn't the only icon from the '80s who is fighting to establish himself anew in the '90s. After more than a month off to retool his series, Bill Cosby is back with a revamped version of "The Cosby Mysteries" -- new producers, fewer supporting players -- and with only these few weeks in which to make his mark before NBC decides which shows to renew for fall. NBC.
* "The George Wendt Show" (8 p.m.-8:30 p.m., Channel 13) -- Oddly enough, the very success of "Frasier" has affected this series in some very obvious ways, beginning with the fact that its original premise -- loosely based on the National Public Radio "Car Talk" brothers -- has been played down to avoid comparisons with the radio arena of "Frasier." That's ridiculous, because "The George Wendt Show" will be compared with "Frasier" no matter what. The pressure's on -- except for Pat Finn as younger brother Dan to George's George, who is in a no-risk, low-profile co-starring position. CBS.
* "Due South" (9 p.m.-10 p.m., Channel 13) -- Good show, new time -- and this is an even tougher time slot. CBS.
* "Northern Exposure" (10 p.m.-11 p.m., Channel 13) -- In this episode, Chris (John Corbett) is given oral exams by two University of Alaska professors, one of whom thinks he's full of hot air -- and based on his dialogue, it's hard to disagree. CBS.
* "Choices of the Heart: The Margaret Sanger Story" (9 p.m.-11 p.m., LIF) -- The producers of this 1995 Lifetime movie seem either unconcerned or unaware that this same story was told, and told much the same way, in a 1980 CBS made-for-TV movie called "Portrait of a Rebel: Margaret Sanger." Bonnie Franklin played the pioneering birth-control advocate in that drama, and Dana Delany, formerly of "China Beach," plays her in this one. Repeated at 11 p.m.