LOS ANGELES?The race for the Oscars goes into overdrive here Tuesday when nominees for Hollywood's most coveted awards are unveiled with the best picture battle shaping up to be a David and Goliath showdown.

The identities of Oscars contenders will be revealed before hundreds of media shortly after 5:30 am (1330 GMT) at the Academy of Motion Picture Arts and Sciences' Samuel Goldwyn Theater in Beverly Hills.

All eyes are on the race for best picture, where low budget Iraq war drama "The Hurt Locker" is rapidly emerging as the favorite to thwart James Cameron's science fiction blockbuster "Avatar", the most expensive film ever made.

The contrast between the two films couldn't be more stark.

Cameron's film -- with a reported budget of $500 million -- had been an early favorite after rewriting the box office record books, earning more than $2 billion to become the highest grossing film in history.

Yet it is "The Hurt Locker" -- directed by Cameron's ex-wife Kathryn Bigelow -- which has become a surprise contender in the best picture race after winning a series of awards, indicators that augur well for the March 7 Oscars.

As a commercial venture however the film has barely broken even, earning just $16 million worldwide after costing around $15 million.

Yet Bigelow's tense drama about a maverick US Army bomb disposal expert in Iraq has been a critical darling, winning a series of prizes and accolades so far this year.

The latest of those came on Saturday when Bigelow pipped Cameron to the Directors Guild of America (DGA) Awards top prize, the first time a woman has ever won the award.

In 62 years, only six winners of the DGA award have failed to go on and win the corresponding best director Oscar -- and the directing Oscar often goes to the film which wins best picture.

Bigelow's film also scored a surprise win at the Producers Guild of America Awards in January, another reliable Oscars barometer.

"I don't think there's any doubt that 'Hurt Locker' is the new front-runner," said Pete Hammond, Maxim magazine film critic and an awards season pundit for the Los Angeles Times.

"Winning the DGA awards is usually a good omen, and it bodes well for best picture. It's in good shape but 'Avatar' is the big challenger," he added.

Oscars organizers doubled the number of best picture nominees in a move analysts have said was intended to help boost television ratings for the awards show, which increased by 13 percent in 2009 after hitting a record low in 2008.

The expansion of nominees could see a number of interesting sub-plots unfold, with Pixar's "Up" likely to be only the second animated film to win a best picture nomination.

There is also the possibility of science-fiction -- a genre traditionally ignored at the Oscars -- being well represented, with "District 9" and "Star Trek" both outside bets to join "Avatar" on the shortlist.

While the best picture race is close, the competition for the coveted acting awards is starting to acquire a look of inevitability.

Popular Hollywood veteran Jeff Bridges is the heavy favorite in the best actor race after already winning a slew of honors for his portrayal of a washed up country singer in the drama "Crazy Heart."

Bridges's likely rivals are expected to include George Clooney for "Up In the Air," Morgan Freeman for "Invictus" and Colin Firth for "A Single Man."

In the best actress stakes, Sandra Bullock has emerged as a front-runner after winning at the Golden Globes and Screen Actors Guild Awards.

Bullock's accolades have come for her performance in "The Blind Side," where she plays a southern housewife who takes in homeless black teen Michael Oher, who goes on to become an American football star.

However, Bullock is expected to face stiff competition from perennial Oscar favorite Meryl Streep, who is tipped to pick up her 16th Academy Award nomination for her performance in "Julie & Julia."

In a bizarre twist, Bullock may become the first actress in history to win an Oscar and a Razzie -- the annual parody of the Academy Awards -- in the same year. On Monday Bullock was nominated for her performance in the comedy "All About Steve."

In the supporting acting categories, "Inglourious Basterds" star Christoph Waltz and Mo'Nique of the drama "Precious" are favorites.

Tuesday's nominations announcement takes place at 5:38 am (1338 GMT) local time.