A BIG-mouthed extra working on the new “Indiana Jones” flick has blown his fledgling movie career to smithereens by spilling the film’s major plot points.

Director Steven Spielberg and producer George Lucas made the entire cast and crew of “Indiana Jones and the Kingdom of the Crystal Skull” sign nondisclosure agreements. But Tyler Nelson – cast as a “dancing Russian soldier” – gave an interview to his hometown newspaper, the Edmond Sun in Oklahoma, in which he revealed that: CLICK ON MORE TO FIND OUT! SPOILER!!

* Indy, played once again by Harrison Ford, and the Soviet army are both searching for a priceless skull made of crystal in the jungles of South America.

* The Russians take Indy hostage and then blackmail him by threatening to kill his ex-girlfriend and mother of his son, Marion Ravenwood, portrayed by Karen Allen. Cast as the son is Shia LaBeouf.

* Cate Blanchett plays an evil Russian who grills Indy. “I saw Harrison Ford strapped to a chair and being interrogated,” Nelson told the paper.

Nelson’s own big scene comes when he celebrates Indy’s capture by dancing to balalaika folk music. But it’s doubtful the footage of the 24-year-old actor – a professionally trained ballet dancer who studied at the Bolshoi Academy in Moscow – will make it into the final cut. Spielberg, furious Nelson blabbed, has reportedly snipped his scene.

Spielberg’s spokesman, Marvin Levy, wouldn’t say whether any of Nelson’s spoilers are accurate, but noted: “Who knows whether that particular person will ever work in this town again?”

Reached by Page Six yesterday, Nelson told us, “No comment. I’m not supposed to talk about it.” But his rep at the Thomas Talent Agency said, “He’s in trouble. He’s got to know that he can’t do that.”

Meanwhile, there have been behind-the-scenes machinations to get the story squashed. Nelson got the Edmond Sun to yank the story from its Web site, with an employee there telling us: “We removed it out of respect to a hometown boy.” And plot-spoilers posted on Harry Knowles’ influential Ain’t It Cool News site also vanished. Knowles didn’t return our call.

The movie, fourth in the “Indiana Jones” series, is set to hit theaters in May.

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