Allison Janney says playing a character in an animated film is an actor’s dream.

“You don’t have to worry about how you look. You can just go in your PJs and have fun without any pressure,” says the Dayton native who plays the starfish, Peach, in “Finding Nemo 3D.” The 2003 animated film was re-released on the big screen in 3D this weekend.

The underwater adventure, which won the 2003 Academy Award for Best Animated Feature, centers around a clownfish named Nemo and his overprotective father. In the film, the two become separated in the Great Barrier Reef when Nemo is unexpectedly taken far from his ocean home to a fish tank in a dentist’s office. That’s where he meets Janney’s character, Peach.

At Monday night’s premiere at Hollywood’s El Capitan Theatre, Janney saw the film for the first time since it opened in 2003.

“It’s magical, like you’re all sitting in the ocean with the characters swimming around you,” she said of the new 3D version. “It’s so much fun!”

Because each character was recorded individually, Janney says the premiere was also the first time she had gotten together with many of the other actors who appear in the film. Marlin, Nemo’s dad, is voiced by Albert Brooks, Nemo by Alexander Gould and Nemo’s friend Dory by Ellen DeGeneres.

“I passed Ellen DeGeneres walking in and out of the sound booth,” Janney remembers. “You go through the script with different line readings — over and over for the director and the engineers. They show you some of the animation in its early stages — black-and-white sketches.”

Director Andrew Stanton had seen Janney on TV’s “West Wing” and wanted her to use her natural voice for Peach.

In addition to “Finding Nemo,” Janney is currently appearing in two other films:

• She plays an across-the-street neighbor, Carol Ostroff, in the comedy “The Oranges” with Hugh Laurie and Catherine Keener that opens Oct. 5.
• She portrays a cynical professor of British Romantic Literature in Josh Radnor’s film “Liberal Arts,” now playing in select markets.

Set at a small liberal arts college, the Radnor movie was filmed at Kenyon College, Janney’s and Radnor’s alma mater.

“It was fantastic to be back there,” Janney said. “It’s such a bucolic, extraordinarily beautiful campus, and even though it was summer, I got to see some of my professors.”

A theater history major at Kenyon, Janney was cast in her first play freshman year by Paul Newman, who had also attended Kenyon. Newman and his wife, Joann Woodward, encouraged her to study at New York’s Neighborhood Playhouse. She made her Broadway debut in Noel Coward’s “Present Laughter” and earned the Outer Critics Circle Award and Clarence Derwent Award for her performance.

Janney, who won four Emmy awards for her portrayal of White House Press Secretary C.J. Cregg on “The West Wing, has been busy filming two projects over the summer — a modern retelling of Anton Checkhov’s “The Sea Gull” with William Hurt, and “The Way, Way Back,” the Steve Carell-Toni Collette comedy-drama.

Her decision to accept a particular role, Janney says, depends both on the people she’ll be working with as well as the script.

“If I like the script, I’ll meet with the director and I’ll do it,” said Janney, who explained that lower-budget independent films often have better roles for her.

Other projects, Janney said, include supporting animal charities and doing voice-overs for organizations such as Heifer International. But with such a hectic work schedule, she says it’s hard to find time for other things.

Which helps explain why it’s been a while since she’s visited her hometown.

“I haven’t been back to Dayton in a while,” said Janney, a graduate of The Miami Valley School. “But I’m hoping to come back soon.”