Matt Groening's initial concept began as a brief cartoon sketch on a mostly forgotten television show. Then it expanded to a half hour and became an enormous hit, the longest-running TV situation comedy in history. It took almost 20 years for the cartoon to reach the big screen, however, which makes "The Simpsons Movie" simultaneously both unlikely and inevitable. In the course of that long, circuitous journey the many contributors to the series pushed the boundaries of its various contexts - cartoon, sitcom, satire -in new directions, expanding the possibilities of the animated cartoon far beyond its form's traditional style and content.

With the show's typical mixture of gleeful cynicism and clever allusion, the movie opens with a brief, extremely violent sequence from "The Itchy and Scratchy Show," the cartoon within the cartoon, preceding the credits, then settles into its purported subject of environmentalism. The rock band Green Day, performing on a barge in the middle of Lake Springfield before an appreciative crowd, pleads for Springfielders to care about pollution, which naturally inspires them to boo and throw all sorts of projectiles. As the band's barge, eaten away by the toxic water, slowly sinks, the musicians exchange their guitars for violins and play "Nearer My God to Thee," the hymn the ship's orchestra famously played as the "Titanic" sank gracefully into the North Atlantic.

Although it proceeds like an extended version of a typical episode, no other moment in "The Simpsons Movie" matches the wit of that scene. Its complicated plot follows the theme of environmental awareness throughout, beginning with Grandpa Simpson's cryptic prediction of doom, Lisa's slide show based on Al Gore's "An Inconvenient Truth," Homer's disposal of pig manure in the cleaned-up Lake Springfield, and the machinations of a greedy head of the Environmental Protection Agency. Homer's toxic gesture inspires the EPA to enclose the town inside a transparent dome, precipitating a crisis in Springfield, the Simpsons' narrow escape from the angry citizens, and a journey to Alaska.

Aside from that basic situation, most of the movie combines familiar elements from dozens of the television shows. The pious, saccharine neighbor, Ned Flanders, shows obnoxious Bart that fathers and sons can enjoy a relationship different from the ongoing bullying and hostility he experiences with Homer. Lisa falls in love with an Irish lad who shares her environmental concerns, and little Maggie, diapers, pacifier and all, ultimately helps to save the day.

Again, in the manner of the TV show, a series of occasionally crude, often misanthropic gags enrich the movie. Homer and Bart dare each other to perform dangerous, outlandish stunts, including Bart's naked skateboard ride through the streets of Springfield; the EPA's announcement of Springfield's doom sends the church congregation rushing to Moe's Bar, while the barflies all flee to the church, demonstrating the town's two sources of consolation. In a parody of both "Spider-Man" and "Charlotte's Web," Homer initially names his pet pig Spider-Pig, then puts glasses on the animal and appropriately dubs him Harry Plopper.

Despite its far greater length, the picture oddly omits a number of Springfielders, including Apu, who runs the convenience store, and the strange and sinister Sideshow Bob, and barely touches on some of the other regulars, like the mayor, the school principal, and Mr. Burns, the wealthy owner of the nuclear power plant that gives the town its special glow.

But "The Simpsons Movie" remains faithful to the spirit of its remarkable original in its presentation of Homer, probably the only cartoon example of Marx's Lumpenproletariat, and his fellow citizens, who perfectly embody H. L. Mencken's booboisie. Although it slips in a number of satiric bits and sight gags, it actually employs fewer allusions to its typical mixed bag of high and low culture, which can often feature sly references to Michelangelo and Michael Jackson, Proust, Picasso, and Pee-wee Herman, "Paradise Lost" and "Debbie Does Des Moines." The feature-length version of an idea that began so oddly so long ago should nevertheless please its millions of fans with a truer depiction of American family life than we usually see on television or even in the movies.

"The Simpsons Movie" (PG-13), directed by David Silverman, is now playing at area theaters.