When “The Simpsons” hit its 200th seg in 1998, exec producer David Mirkin opened up the episode’s table read with what he calls a “sick, sick joke.”

“Our 200th episode … halfway there,” he quipped in a weary voice.

The quip cracked up the room — and elicited a few groans. Few series ever make it to 200 episodes – so there was no way “The Simpsons” would actually produce another 200 episodes after that, right? Right?

Fast forward nine years. Now in its unprecedented 18th season, “The Simpsons” will celebrate its 400th episode this May.

Mirkin and several of “The Simpsons'” producers and directors — as well as Bart voice Nancy Cartwright — closed this year’s William S. Paley Television Festival on Thursday night, in front of a packed house at the Directors Guild of America.

Led by creator Matt Groening, the group discussed the show’s origin, its impact on pop culture and its astounding longevity.

“There’s an incredible passion among the staff,” said Groening, who pointed out the longevity of many staffers on the show. “This is a collaborative effort.”

The “Simpsons” team credited the show’s ability to tap into several forms — from drama to sci-fi to horror to satire — and its cast of a thousand characters, all of which keep the animated skein fresh.

“The characters don’t age,” added exec producer Al Jean, who remembered being creeped out by the last few seasons of “Leave It to Beaver,” when the kids weren’t really kids anymore.

The producers also credited their virtually unlimited amount of freedom in putting together the show. Given the fact that “The Simpsons” has generated billions of dollars through the years to News Corp., the show receives minimal interference from the network (Fox) or studio (20th Century Fox TV).

Exec producer Matt Selman also noted that there are always new targets ripe for satire on the show.

“As long as horrible things happen,” he quipped, “The Simpsons” will be on the air. “We’ll probably last until the end of the world.”

Panel also included director Mark Kirkland, exec producers Tim Long, Ian Maxtone-Graham and consulting producer Carolyn Omine.

Other tidbits:

  • “The Simpsons” runs like a well-oiled machine, with 20 writers and two rooms operating at the same time. The large staff was what allowed the show to continue in production while simultaneously producing this summer’s highly anticipated “The Simpsons Movie.”

    The movie is only finally happening now, added Jean, because the technology is finally available to make the movie the producers had hoped to make.

    “Digital animation, digital editing, the technology is much better than it was 10 years ago,” Jean said. “We couldn’t do it until recently.”

  • The writers’ favorite characters? It goes through waves, but at the moment, the scribes appear to be obsessed with middle-aged loser Gil. They’re frustrated that the character hasn’t caught on with viewers.

  • “At least half the cashiers at Amoeba (Records) have ‘Simpsons’ tattoos, but I don’t get a discount, though,” said Groening.

  • Among the celebs who have turned down roles: Jon Bon Jovi, Tom Cruise and Smokey Robinson.

  • Paul McCartney agreed to appear on the show, but first demanded that the producers keep Lisa a vegetarian for as long as “The Simpsons” remains on the air. Groening and company said they occasionally run into McCartney, who still holds them to that pledge.

  • The strangest “Simpsons” product Groening ever signed off on? Bart Simpson asthma inhalers.