Most of the time, when I see an ad touting a ''special guest star'' on a series I enjoy, my first thought is, There's one show I can cross off my list this week. Stunt casting usually results in labored laughs in a sitcom -- the show's regular cast members have to abandon their usual interlocking comic rhythms, and the writers tend to slow down the pace to trundle in a plotline that'll accommodate the bedazzling visitor. I still shudder when I think about Kathleen Turner playing Chandler's cross-dressing dad on Friends. On the other hand, the same show turned Tom Selleck into a charming romantic lead for Courteney Cox Arquette, and more recently, who knew Alec Baldwin could still crank up the energy to elicit guffaws as an avidly overbearing suitor for Lisa Kudrow's Phoebe?
Of all the shows that inject guest stars like so much human collagen to puff up their ratings, Will & Grace seems to do it with the most, well, grace. Not that the sight of Michael Douglas boogying down to ''Get Ur Freak On'' during this week's W&G is graceful. But the whole point of the scene -- in which Douglas plays a closeted cop who wants to score with Eric McCormack's Will, and takes him to a gay bar to seduce him -- is to make Douglas' character look like a middle-aged doofus. Douglas stays admirably in the moment; his wiggling to Missy Elliott's rhythm track is both hilarious and scary to behold. The basic notion of confused sexual identity has become a standard ploy in this series -- think of Matt Damon's spunky appearance earlier this year as a straight guy posing as homosexual and competing with Jack (Sean Hayes) for a spot in a gay men's choir. The show is endlessly imaginative in the ways it explores themes like this with a humor that doesn't betray or belittle its core gay characters. In fact, it's only when Will has to drop the wisecracks and become sincere in dealing with his parents' ludicrously loveless marriage (Mom and Dad are played by -- again with the guest stars -- Blythe Danner and actor-director Sydney Pollack) that the show seems strained.
Will & Grace has been chockablock with guests both big and small this season, and the results have been almost invariably funny. Rosie O'Donnell popped up recently as the mother of Jack's son, Elliot, and on W&G's April 4 episode, Eileen Brennan turned a small role as Jack's acting teacher into an instant portrait of a hard-bitten old bat whose teacherly gifts long ago ossified into showbiz cynicism. In this week's Douglas episode, former Saturday Night Live member Molly Shannon reprises her role as a cuckoo neighbor, Val, and she's terrific, addled by a mean-spirited obsession to drive Debra Messing's Grace as loopy as she is. In a way, what the guest stars do for this particular series is take some of the pressure off the regular cast (which also includes Megan Mullally as Karen). Under the constant, inspired direction of James Burrows, this is probably the hardest-working quartet on TV, called upon to do as much wild physical humor as they are to deliver risque lines (such as Grace referring to Jack spending an evening with ''three hot guys'' as a ''fourgy'') without overselling either the pun or the innuendo.
Rarely does a TV show pull off guest-stuffing as adroitly as Will & Grace. It remains to be seen how upcoming stunts like Tim Conway and Vicki Lawrence showing up as Anthony Clark's parents on the May 6 episode of Yes, Dear will fare, or whether Scrubs can comedically accommodate an April 30 visit from four members of an older hospital show, St. Elsewhere (William Daniels, Ed Begley Jr., Stephen Furst, and Eric Laneuville -- what, Howie Mandel was busy?). But I'm actually looking forward to the King of Queens' use of Ben Stiller on May 20. Stiller, real-life son of costar Jerry Stiller, who plays Arthur, will play Arthur's father in a wacky flashback. That's the kind of stunt casting that usually sends me out of the room holding my about-to-burst head, but given how clever Queens can be, it might be worth risking a peek.