The universe of “The Simpsons” — outlandish, yellow and absent of normal human growth — has sketched with parodying perfection the struggle of family life, the exploitation of a neighbor’s good will and the bizarre qualities of school bus drivers, to name just a few of its accomplishments.

In one of its greatest episodes, about Prohibition, Homer’s concluding toast demonstrated how the animated series could be as damning as it was hilarious: “To alcohol, the cause and solution to all of life’s problems!”

“The Simpsons Movie” arrives a decade after that 1997 episode, and long after the show’s glory days. Not to sound too much like the Comic Book Guy, but the Fox sitcom, which once brilliantly satirized TV’s conventions, has gradually settled into its own ruts — which usually entail Homer acting silly for silliness’ sake.

After 18 seasons on television, the much-anticipated big-screen debut of “The Simpsons” feels purposeless — as if creator Matt Groening finally thought: “Well, we might as well.”

The movie quickly revels in lampooning itself. Ralph Wiggum crawls over the opening 20th Century Fox logo. An “Itchy and Scratchy” segment then plays out before revealing the Simpsons family watching, seated in a movie theater.

“I can’t believe we’re paying for something we get for free on TV!” exclaims Homer (voiced by Dan Castellaneta).

An alteration of the show’s opening sequence leads to a Green Day concert where the band tries to speak about pollution, thereby setting up the action: Lake Springfield, it turns out, is a polluted mess, the result of — among other things — Krusty the Clown dumping tankfuls of his flop sweat into it.

Homer ruins a cleanup effort, however, emptying a silo (yes, a silo) of pig feces in the lake, the result of his new best friend: the adopted Spider-Pig, who’s later renamed Harry Plopper. This isn’t Homer’s first love affair with a potential meal, nor his only go-around with a pig. Fans will recall his “pig-de-la-resistance” in “Lisa the Vegetarian,” the excellent 1995 episode in which vegetarianism is tackled more successfully than pollution is here.

Lake Springfield promptly turns black and the Environmental Protection Agency, led by Russ Cargill (Albert Brooks), soon intervenes, placing a giant, transparent dome over Springfield and its townspeople. It’s a clearly redundant entrapment for a town that exists everywhere and nowhere. (At one point, standing atop a mountain, Ned Flanders points to the states bordering Springfield: Ohio, Maine, Kentucky and Nevada.)

Cargill — who sounds a lot like Hank Scorpio, the maniacal but cheery evil genius Brooks voiced in a 1996 episode — works for President Arnold Schwarzenegger (Harry Shearer) who declares: “I was elected to lead, not to read.”

Homer must save the town from Cargill’s plans for Springfield, but, more importantly, he has to win back the trust of Marge, Bart, Lisa and Maggie.

The plot is wayward at times — particularly a trip to Alaska that feels excerpted from an unaired episode.

But narrative was never what drove “The Simpsons.” It was always the jokes, which are just as relentless here as they are on the show.

Under director David Silverman’s stewardship, the animation is brighter and filled with more background detail. Every character now maneuvers with a carefully drawn shadow.

Little has changed in the leap to the big screen, but we do gain a new perspective on Springfield, where Mr. Burns’ house is now so elevated it seems more like the Grinch’s lair hovering above Whoville.

We also see for the first time Milhouse’s neighborhood and Bart’s bathing suit area. His full-frontal scene is one of the movie’s best visual gags.

While “The Simpsons Movie” is — like the TV show has become — too much a caricature of itself, it still possesses good cheer, an aversion to self-seriousness and manic energy for stuffing the screen with layers of humor.

In one of the final scenes, Homer again finds himself soaring across Springfield Gorge as he did in the 1990 “Bart the Daredevil” episode. On the other side of the gorge, moviegoers will notice an old ambulance from that episode crashed against a tree — as though it’s been sitting there in SimpsonLand for 17 years.

The small artifact of animation recalls both the show’s bygone triumphs and stubborn resilience.

“The Simpsons Movie,” a 20th Century Fox release, is rated PG-13 for irreverent humor throughout. Running time: 87 minutes. Two and a half stars out of four.