It Came from Outer Space

Skirt blowing in the breeze, 6'4'' John Lithgow sashays down the corridor of a Studio City, Calif., soundstage, smoothing bunched-up nylons and wiping marigold wisps of wig from his face. His thickly glossed lips ease into a self-conscious smirk as he glides past Jane Curtin into a dressing room and closes the door. ''I wouldn't go in there,'' Curtin tells a cluster of onlookers. ''It's not a pretty sight. Kind of like a butterfly turning back into a caterpillar.''

Curtin's warning seems superfluous. After all, startling transformations are nothing new here on the set of NBC's latest hit comedy, 3rd Rock From the Sun, a show whose out-of-the-blue success startled everyone, including its network. ''We weren't convinced we could go in and own a time period against ABC on Tuesday nights,'' says a giddy NBC Entertainment president Warren Littlefield. ''But in fact, that's just what we're doing.''

3rd Rock rocketed out of the gates on Jan. 9, soaring to seventh place in the ratings, and has finished first in its 8:30 time slot ever since. (It also outdraws its competition in key demos, including teens and 18- to 49-year-olds.) Granted, the show has the advantage of great placement — sandwiched between Wings and Frasier. But unlike those other well-situated NBC hits, The Single Guy (which follows Friends) and Caroline in the City (which tails Seinfeld), 3rd Rock builds on its established lead-in rather than jettisoning a few million viewers.

It differs radically in another important way, too. 3rd Rock (in case you've been living under a, well, rock) doesn't deal with the dating habits of twentysomethings, but rather the antics of a quartet of aliens who have assumed human form to study life on Earth: Dr. Dick Solomon (Lithgow), the brash mission leader posing as a physics professor; Sally (Kristen Johnston), the second-in-command, trapped in the body of a six-foot blond bombshell; Tommy (Joseph Gordon-Levitt), an elderly information officer-turned-14-year-old boy; and Harry (French Stewart), a flake in this world or any other. Curtin plays Dr. Albright, the prim Pendleton University professor Solomon yearns to probe.

An unlikely group to feel passionate about, but America seems to be hooked, and 3rd Rock's creators are hard-pressed to explain the allure. ''I don't know why the reaction to the show is so big,'' says Bonnie Turner, who created and executive-produces the Carsey-Werner sitcom with husband Terry. ''But if I could plant a kiss on John Q. Public, it would be a big wet one.''

Well, we have our own little theory. The perfect union between NBC and this otherworldly sitcom seems to share several key elements with a certain wedding-day tradition.

SOMETHING OLD (as in ''nanu nanu'')
An alien sitcom is hardly a novel concept. ''Every 10 years there's one,'' says Littlefield. ''My Favorite Martian in the '60s, Mork & Mindy in the '70s, and ALF in the '80s. The stranger in a strange land is a wonderful, classic notion that works.'' And 3rd Rock remains true to the satirical bent of outsider looking in while managing to be sexier than Martian, raunchier than Mork, hipper than ALF, and more sophisticated (by a hair) than Coneheads. The challenge for the creators is to stay fresh; Martian, Mork, and ALF quickly jumped into the top 20 but stumbled after a year or two. ''The aliens can discover something every week, just as we do,'' argues 3rd Rock staff writer Christine Zander. ''And eventually they might get in trouble for liking this planet too much.''