LOS ANGELES (Reuters) - The new instalment in the Star Wars movie saga opens in theatres this month against a formidable force: the galactic hopes of devoted fans who have waited a decade to revisit their beloved universe of Jedi, droids and lightsabers.

Can The Force Awakens meet those expectations when it debuts on Dec 18?

"No," said director J.J. Abrams. "How can anything live up to any expectation like that?" What the movie will offer, he told Reuters, is great performances and visual effects, music "that breaks your heart and soars", plus a story, characters and creatures that are new, but feel like they fit in the universe created by George Lucas in the original 1977 film.

"George was creating a world that we wanted to go back to in order to tell a story we'd never seen yet," Abrams said. "In a way, we were going backward to go forward."

For example, he said, the film-makers created droids "to feel completely new and different and at the same time, something that was so of Star Wars." He added: "That was always the challenge."

Lucas bowed out of Star Wars after he sold his film studio to Walt Disney Co in 2012 for US$4 billion. "There's no way that I can imagine anything touching the magic of what he did," Abrams said, "and yet we all did the best we could to make that happen."

Set 30 years after Return Of The Jedi, the new movie brings characters Luke Skywalker (Mark Hamill), Princess Leia (Carrie Fisher) and Han Solo (Harrison Ford) back to their galaxy far, far away. Newcomers Rey (Daisy Ridley) and Finn (John Boyega) lead a younger generation that grapples with the conflicts that haunted the past.

Disney is guarding details about the film's plot. The secrecy has stirred rampant online speculation, particularly about the fate of Skywalker, who is absent from trailers and posters promoting the new film.

Abrams said the character was purposely left off to keep key parts of the story under wraps. "It's just what our narrative is," he said, "so if it's driving anyone crazy, apologies. But it's mostly about wanting to protect the experience for the people who might go see the movie."

Ridley, who plays a scavenger, said the film captures the "delightful" tone of the earlier movies. "Star Wars never had like insane violence or anything," she said. "It's always joyful and always uplifting even though bad things happen."

Force Awakens also features "classic Star Wars humour, choppy dialogue," said Boyega, who described his role as a conflicted Stormtrooper.

Adam Driver plays Kylo Ren, a character dressed similar to Darth Vader who is presumed to play the main villain, though that depends on the perspective. "I don't think he's evil at all," Driver said. "I think he's right."

Aside from fan anticipation, the movie faces lofty box office projections for the opening weekend, from US$170 million (S$237 million) to US$220 million in just the United States and Canada, a level never achieved in December. Jurassic World holds the record with US$208.8 million last June.