So the huge investment behind "Avatar" rides on Cameron's wild imagination and the technology he developed to put it on the screen.

"Here's the thing. No one knows if you've got the turkey that lays the golden egg or you've just got a turkey," Worthington said. "We're all trying to be cool, calm and relaxed about it, but inside, I think all of us are sweating bullets.

"But you've got to stand by the fact that what we've done is push the envelope again, thanks to Jim. ... I'm sure people are hopefully going to enjoy going on this ride, because to me, he took me to Pandora. Now he's going to take the rest of the world."

Worthington stars as Jake Sully, a paralyzed former Marine recruited to take his dead brother's place in the Avatar Program, inhabiting a genetically engineered body mixing human and Na'vi DNA so he can survive on Pandora.

Jake winds up in an unlikely romance with Saldana's Neytiri, a member of the spiritually- and ecologically minded natives, who like Aborigines in our own history face conflict with militant humans greedy for their resources — in this case, Pandora's supply of an energy-rich mineral called unobtainium.

Unlike native populations that succumbed to European colonialism, the Na'vi can give as good as they get.

"You're not encountering inhabitants that are 4-foot-9 and are completely defenseless. These (people) will kill you in a second," said Saldana, whose Neyteri is an expert hunter. "They're not victims, I'll tell you that. They can't be. They're warriors."

Cameron conceived the story in 1995 then waited a decade for technology to catch up so he could film it.

During that time, Peter Jackson mastered the art of performance-capture filming with his Gollum character in "The Lord of the Rings" saga and the giant ape in "King Kong" — both roles played by Andy Serkis, whose motions were recorded by digital cameras then topped off with intricate computer imagery to create the finished product.

With "The Polar Express," "Beowulf" and this season's "A Christmas Carol," Robert Zemeckis pioneered shooting entire films in performance capture, actors working on bare sound stages in skintight suits dotted with sensors read by the digital cameras. Computer animation filled in the costumes, sets, props and other details.

Zemeckis' films have the look of animation, but Cameron set out to create a photorealistic world filled with alien lifeforms — giant plants with a defense mechanism that sucks them into the ground in an instant, flying reptilian "banshees" that can be ridden like horses, six-legged beasts of burden called "direhorses."

Along with Cameron's 3-D system, among his innovations were a virtual-camera simulating what the finished product might look like as he was filming and a helmet-cam clamped to actors' heads to record their facial expressions, overcoming the "dead-eye" effect and other limitations that have made the faces of some performance-capture characters seem lifeless.

"So here you've got four or five new technologies all laid over each other in this palimpsest of new technologies, and it was just insane for the first six months or so," Cameron said. "We literally were just scratching our heads every day, which is a wonderful place to be as a filmmaker. To be 25 years into a career and be standing on the set going, `I don't know what ... we're doing.'"

Cameron hired Jackson's WETA effects house to transform his digital data into the world of Pandora — basically, to put the costumes and makeup on the characters and build the sets.

Based on about 30 minutes of footage Cameron showed reporters in advance of "Avatar's" Dec. 9 world premiere in London, the results are mind-blowing. The Pandora segments and the Na'vi seem as real as the human world in the film's live-action segments, with Saldana and Worthington's alien incarnations showing remarkable expressiveness.

Cameron has ideas for two sequels should "Avatar" make enough money to become its own franchise. But that's in the audience's hands now.

"The thing I feared most about this film was that because it wasn't a franchise picture and it wasn't based on something that already was imprinted in the public consciousness, that they just wouldn't know what we were or that we existed," Cameron said. "Fairly early on, we were able to create a pretty high profile for the movie as this kind of mysterious thing, and then it seemed like the more we revealed about it, the more kind of excitement and buzz around it, positive and negative, that there was.

"But the more people are talking, the more they've got to resolve the issue for themselves by going to see the movie."