By BROOKS BARNES

LOS ANGELES - Figuring out which film will win the Academy Award for best animated feature is usually easy: pick the one made by Pixar.

But this year, unexpectedly, animation is becoming a hotly contested race.

The biggest reason is “Fantastic Mr. Fox,” Wes Anderson’s quirky adaptation of the Roald Dahl novel. The film, from 20th Century Fox and the producer Scott Rudin, is attracting a surprising amount of awards attention. “Up,” Pixar’s 3-D flying-house adventure, dominated the multiplexes last May and seemed to be the clear choice for the animation Oscar as recently as a few weeks ago.

Then a fox snuck into Pixar’s henhouse.

“Fantastic Mr. Fox,” which features the vocal talents of George Clooney and Meryl Streep in a story about a dapper family man who can’t resist stealing chickens and cider, arrived in wide release in the United States on November 25. It cost just under $40 million to produce and sold $20 million in tickets - making an Oscar run seem unlikely.

But “Up,” which has been estimated to cost $175 million, earned $293 million in North America and won the Golden Globe award for best animated feature film on January 17, lost two influential awards to “Fox.”

In mid-December , both the New York Film Critics Circle and the Los Angeles Film Critics Association named “Fantastic Mr. Fox” the best animated movie of 2009. Similar awards from five other critics’ groups followed.

“Nobody saw this coming,” said Jerry Beck, the author of 12 books on animation and an operator of the news blog CartoonBrew.com. “The animation in ‘Mr. Fox’ strikes some people as a bit funky, but the film is indisputably a piece of art - something that exhibits a really strong point of view from beginning to end.”

Many critics have been impressed that Mr. Anderson, whose other movies include “The Royal Tenenbaums” (2001) and “Rushmore” (1998), is thriving in a genre entirely new to him. “Fantastic Mr. Fox” was made using stop-motion animation, a painstaking process involving handmade models.

“It’s as if Wes finally found the perfect style through which to channel all of his obsessions,” said Scott Foundas, a former film critic for LA Weekly and now an associate programmer at the Film Society of Lincoln Center in New York.

Nominations will be announced on February 2 and the awards given on March 7. In only the second time since the animated feature category was created in 2001, there will be five nominees. In recent years there have been only three.

And “Up,” directed by Pete Docter, remains very much the lead contender for the best animated feature Oscar, a prize Pixar has won four times.

Many awards strategists consider “Up” a strong candidate for a best picture nomination, especially with that field expanded to 10 nominees this year. No animated movie has ever won in that category, and only one, “Beauty and the Beast,” has been nominated.

Wes Anderson on the set of “Fantastic Mr. Fox,” made with stop-motion animation. / GREG WILLIAMS/FOX SEARCHLIGHT PICTURES