America's yellow-hued, long-running sitcom family "The Simpsons" expands its empire to the big screen Friday when "The Simpsons Movie" hits theaters nationwide. But it almost happened much earlier in the TV show's 400-episode, 18-year run.

"We had a critical moment in the third year where we had an episode that, if we added to, we thought it would be a great movie," said executive producer James L. Brooks. "It was 'Kamp Krusty.' Then we said, 'We're a television show!' And that shut us up for a long time."

But two years ago, the idea of a movie resurfaced. And since then, the project has been largely shrouded in mystery.

"It's cinematic in its story lines, it's a bigger, more emotional story than we're able to do in 30 minutes, and the animation is feature animation," said executive producer Al Jean. "The goal is to have a movie that people will love, even if you've never seen the show, and it's such a great way to get people re-excited about the show after 18 years. It's just so thrilling to have something where people are looking forward to it. Thrilling and daunting."

Daunting, of course, because die-hard "Simpsons" fans can be scathingly critical of the series, frequently arguing whether it's as good as it used to be, the high and low points, etc.

"To us, it's like if you had a vineyard and you had great years and years where it wasn't," Brooks said. "It works like that. It doesn't work in one continuum. I think the last couple years have been among our best."

That statement alone is enough to enrage some fanboys, who are adamant that the show's quality has declined. Before arguing over the movie can begin, here's what we do know:

Previews have already shown a snippet from a scene featuring an angry mob that attempts to include every "Simpsons" character introduced, numbering in the hundreds.

Bart Simpson shows "his private parts" in a scene lasting 1/30th of a second, according to Brooks. "It's extremely innocuous and in no way titillating," he said. "The movie is designed to be a film that viewers of the show can enjoy, including the 10-year-olds who watch the show."

While most TV shows operate just a single writers room, two rooms operate simultaneously on "The Simpsons" with 20 writers at work. Another five or six writers worked primarily on the movie script, but they were all writers who have experience on the TV show.

Although Brooks had not been as intimately involved in the TV show in recent years, he has been active working on the movie. Actor Dan Castellaneta, the voice of patriarch Homer Simpson, said Brooks, the director of "Broadcast News" and "As Good As It Gets," directed the voice actors in the recording studio "like he was on the set of a movie." More time was spent on rewriting and rerecording voices than the production schedule for the TV series allows.

"Simpsons" creator Matt Groening promises the movie won't feel like three episodes of the TV show mashed together.

Groening said Homer is the writers' favorite character because the consequences of his mistakes are bigger ("Bart may get expelled, but Homer may cause a meltdown [at the nuclear plant where he works]"), but the movie will not be Homer-centric. "It's the whole family," Groening said. "But there are a lot of gags with Homer because it's funnier to see Homer get smashed than just about anybody."

After the movie, "The Simpsons" TV show will continue on Fox, and producers will keep striving toward their goal of getting a former American president to record a voice-over.

"The closest we got is we got Tony Blair when he was prime minister," Jean said. "I think there is a little nerve in the American politician's brain that says, 'Don't go on "The Simpsons" ' because we never have been able to quite get that. It's sort of like our great white whale, so maybe it's good that we have this thing that we're always going for. Maybe we'll get it in the next 20 years."

If they do snag an ex-pres, the writers may want to tread more carefully than they did with Jon Bon Jovi, whom Jean said expressed interest in appearing on the show until he read the part that was written for him. Then he declined.

"He didn't like that we covered him with cheese, I think, is the part we wrote," Jean said.

"The Simpsons" has come a long way from its earliest days as an interstitial short on Fox's "The Tracey Ullman Show." The characters look different, and the voices sound different, from those in the first few sketches.

Castellaneta said initially he started with a "Walter Matthau-kind-of-voice" for Homer, but the character's range of emotions required an evolution.

Homer's "D'oh!" began as a script notation calling for an "annoyed grunt."

"Being a big Laurel and Hardy fan, I went back to [Laurel and Hardy foil] Jim Finlayson, who used to go, 'D'ohhhh!' Castellaneta recalled. "But we only had, like, 30 seconds of something, so Matt [Groening] said, 'You've got to speed it up, we don't have that much time. So it went from 'D'ohhhh!' to 'D'oh!' "

If the movie is successful, might fans see the TV family make another trip to the big screen?

"I think we'll have a sequel in about 18 more years," Jean said, "the way that we work."