Butt jokes -- ''Home Improvement'' and ''The Simpsons'' get in on the new trend

Uh, butt’s up, doc? Plenty. Consider television’s cheekiest new trend:

The Sept. 16 season premiere of CBS’ Designing Women offered not one but two semiexposed butt shots of Rusty, the Sugarbakers’ electrician. When Rusty’s loose-fitting pants exposed more than his waistline, Annie Potts crooned, ”When the moon hits your eye like a big pizza pie, that’s amore,” and Julia Duffy got huffy (”Do you really think it’s appropriate this man has no belt?”).

The Sept. 17 series debut of ABC’s sitcom Home Improvement found star Tim Allen’s character, Tim ”The Tool Man” Taylor, offering this fashion tip: ”Hike your tool belt up to avoid that unsightly butt crack.” The derriere jokes didn’t end there; Tim later counseled his young son to avoid displaying a ”baby butt crack” when wearing a tiny tool belt. (This tush talk was a hallmark of the comedian’s stand-up act, seen in last year’s Showtime special Men Are Pigs.)

* On the Sept. 26 episode of Fox’s The Simpsons, dad Homer remarked that cartoons are ”just stupid drawings that give you cheap laughs.” Immediately afterward, he got up from the couch faster than his pants did. Homer’s humongous heinie had Bart doubled over with, yes, cheap laughter.

Is there something strange in the water in Hollywood this season? Or has everyone suddenly taken a cue from the butt skit that started it all, the 1978 sketch on Saturday Night Live in which refrigerator repairman Dan Aykroyd’s drooping drawers inspire bad jokes and howls of laughter from famous nerds Todd DiLaMuca and Lisa Loopner. Todd can’t resist a mention of the ”moon coming out,” and Lisa blurts out, ”No more wisecracks, Todd!”

”There’s nothing funnier than someone’s pants falling down,” explains Designing Women co-executive producer Pamela Norris. ”There must be something down deep in the human character — that infantile quality.”

Where will it all end? No one’s sure, but the news shows are probably safe — as long as those anchors stay behind their desks.