‘Simpsons’ may have lost edge, but is still worth some guffaws

The notion that Fox’s iconic animated comedy isn’t as good as it used to be - that it declined after the second or seventh or 17th season, depending on who you ask - hangs over the hourlong special, which airs tomorrow night at 8:30.

Any TV retrospective has a tough challenge in a nation as obsessed with pop culture as ours, more so when the subject is a phenomenon on the level of Homer and Marge and Bart and Lisa. There’s very little that the special can tell us about “The Simpsons’’ that we don’t already know, despite the best efforts of producer, writer, director and host, Morgan Spurlock.

Celebrities love “The Simpsons’’! Matt Groening is the coolest guy who ever made a gazillion dollars with Rupert Murdoch! People collect “Simpsons’’ stuff! Moby is a nerd!

Not exactly news. OK, the dude with the Tree House of Horror tattoo covering his entire back is a revelation. But the rest underwhelms. Dan Rather and Brian Williams mocking themselves by praising Kent Brockman? Yawn.

So it’s left to the 450th episode, “Once Upon A Time in Springfield,’’ to make a case for the enduring funniness of “The Simpsons,’’ or the lack thereof.

It’s only natural that the once groundbreaking, controversial, and unbelievably fresh show now seems comfortable and familiar. C’mon, 20 years! Even the Rolling Stones ran out of fresh moves after that long.

As in most recent episodes, the humor in Sunday’s show comes rapid-fire in the first act, then slows down for plot resolution. If there’s no moment of genius, there are enough laughs to remind us why we loved this show in the first place. And let’s face it, that’s not something that can be said about every episode these days.

The A story: Once again, the network suits are messing with Krusty the Clown. They bring in Princess Penelope (Anne Hathaway) and her unicorn to make his show more girl-friendly. Lisa loves it. Bart and Milhouse retreat to the fetal position, then begin plotting.

The B story: Mr. Burns ends the free doughnut program at the nuclear plant, so Homer, Lenny, and Carl fall into the clutches of a recruiter from the rival Capital Cities plant.

Now these sound like setups that “Simpsons’’ devotees have seen dozens of times in the previous 449 episodes. Still, when Krusty tells the princess, “I work like I drink - alone, but with a monkey watching me,’’ it’s hard to avoid a spit take.

As always, there is character-based comedy.

Bart: “Poor Krusty, he’s become the lowest form of life! A sidekick!’’

Milhouse: “You said it, Bart!’’

Most important on this night, there’s plenty of the meta-humor that has been a “Simpsons’’ trademark from the beginning. The chalkboard gag during the opening credits has Bart writing, “The world may end in 2012, but this show won’t.’’

The statement seems a little rueful. However strongly the producers defend the show as it is now, they have to know that some of the thrill is gone. Like Mr. Burns, however, Fox’s Rupert Murdoch and his minions will never let it die until there are no more pennies to be squeezed from it.

Like Krusty in the alley behind the studio, “Simpsons’’ fans these days may be sprinkling cheap gin on a couple of slices of white bread and calling it a sandwich. But few of us will stop, at least as long as the monkey is watching.