The film that wasn't supposed to be made -- at least not until the TV series on which it is based wrapped production. But once the realization that their show might never get canceled hit producers of Fox's "The Simpsons," they finally moved forward with "The Simpsons Movie," employing a kind of secrecy befitting a CIA mission. Happily for fans, what has been rumored for years is now almost a reality. And when the film premieres July 27 for a worldwide audience, it will be the culmination of a project that really began -- at least in the minds of its producers -- way back in the early 1990s.

In typical "Simpsons" fashion, the Fox film is being punched up, revised and otherwise tweaked even as these words are read. Series producers are famously obsessed with rewrites and laboring to make each frame as clever and perfect as is humanly possible; not surprisingly, the same tack is being taken with the film.

This is a problem for executive producer Al Jean, who has been simultaneously running the 18th and 19th seasons of "The Simpsons" while overseeing the movie project. He is basically working day and night now, in part because "we wouldn't be able to live with ourselves if the movie weren't up to the standard set by the show," he says.

"The problem at the beginning of the process," Jean says, "is that for 18 years, every writer and producer on this show has had a different movie in his or her head. And we can't release 20,000 different ones. Then there were the fears. What if it bombed and killed our legacy? Nobody wanted to do this just for the money."

While early drafts of the film began in 2001, it really wasn't until 2005 that the project hit the fast track. "We all felt there was a certain hump we needed to get over to really get the movie going," executive producer James L. Brooks recalls. "I'm not sure why, but two years ago it stopped being a mountain to climb."

Brooks and his collaborators at Gracie Films have successfully shrouded the film's plot line in mystery even while whetting the appetites of fans with a theatrical trailer that has managed to give none of the actual plot points away.

What is known is that there are more than 100 speaking parts in the film, taking full advantage of the show's vast character repertoire. Trailers show that an angry mob of Springfield townsfolk confronts the Simpson family and that Homer is attacked by the sled dogs he has whipped a bit too enthusiastically. And while the precise location of Springfield has been kept a long-running secret, God-fearing Simpsons neighbor Ned Flanders reveals to Bart that it borders "Ohio, Nevada, Maine and Kentucky." So, uh, that settles that.

Insiders say that test screenings of the rough-cut film have been met with great enthusiasm though the showcases were convened to determine, through attendee reactions and feedback, what works and what doesn't.

"Yes, we're still tweaking it," Brooks says, "but tweaked is an elegant term for crawling on your stomach while the flak whizzes past your head."

One way or another, the film must be done in time for the premiere. After all, it's a project that's largely seen as flop-proof given the worldwide affection for, and devotion to, the "Simpsons" franchise. "Simpsons" creator and film executive producer Matt Groening, for one, is pretty excited about it.

"Doing a movie based on an existing TV show is a very tough needle to thread," Groening admits, "but you know, for some reason we're very happy with how it's turning out."