WHEN Oscar nominations come down on Jan. 28 – two weeks earlier than usual – it’s likely going to be a big day Down Under: No fewer than three saucy Aussie actresses, as well as a Kiwi juvenile, are poised to join Russell Crowe and the New Zealand-produced “The Lord of the Rings: The Return of the King” in celebrating.

Here’s how the four acting categories look at the moment:

BEST ACTOR

Academy rules say Sean Penn can be nominated in this category only once, and it’s anybody’s guess whether he’ll get it for his superb work in “Mystic River” or “21 Grams” – in the latter, a rare sympathetic role is more of a stretch for him, but “Mystic” will get a much bigger campaign.

He’s not likely to cancel himself out, though.

Past nominee Jude Law also looks like a sure thing as the Odysseus-like Confederate deserter in “Cold Mountain.”

Two slots will likely go to past winners: Crowe as the captain in “Master and Commander,” and Ben Kingsley as an Iranian émigré in the tragic “House of Sand and Fog.”

This looks like the year the Academy will finally give Bill Murray a nomination for his nuanced work as a troubled movie star in “Lost in Translation.”

But because Murray refuses to glad-hand for votes, it’s quite possible the fifth slot will go instead to Viggo Mortensen, who finally comes into his own with a towering performance in the title role of “Return of the King.”

Other possibilities include longtime critics’ darling but never nominated Johnny Depp (“Pirates of the Caribbean”), Peter Dinklage (the dwarf hero of “The Station Agent”) and Jeff Bridges (“Seabiscuit”), as well as Jack Nicholson, who has a shot at a record 13th nomination for “Something’s Gotta Give.”

BEST ACTRESS

Best Actress winner Nicole Kidman will likely get a nomination for her role as a struggling Southern belle in “Cold Mountain,” while her pal Naomi Watts will get her first for being put through the emotional wringer as a drug-addicted widow in “21 Grams.”

Completing the Aussie trinity is former nominee (for “Elizabeth”) Cate Blanchett, whose performance as a doctor searching for her daughter in the Old West in “The Missing” was hugely admired, even if the movie wasn’t – and her work in “Victoria Guerin” and “Return of the King” doesn’t hurt, either.

But the heat in this category right now is with Charlize Theron, a beautiful South African actress who emulated Kidman’s winning strategy with “The Hours” and allowed herself to be deglamorized – to an even more severe degree than Nicole – to play a serial murderer in “Monster” (opening Dec. 24).

The fifth likely contender is the much-admired veteran Diane Keaton, who does her best work in years – and even briefly takes her clothes off – in the romantic comedy “Something’s Gotta Give.”

Also possible are Helen Mirren, who also sheds her clothes, in the comedy “Calendar Girls” (Dec. 19), as well as past winners Jennifer Connelly (“House of Sand and Fog”) and Gwyneth Paltrow (“Sylvia”).

BEST SUPPORTING ACTOR

This extremely competitive category is lead by past winner Benicio del Toro, who does yeoman work as a troubled ex-con in “21 Grams.”

He faces a strong challenge from Tim Robbins, deeply affecting as a pedophile victim in “Mystic River.”

At this point, the front runners for the other three slots would appear to be Albert Finney, as a dying spinner of tall tales in “Big Fish” (opening next Wednesday), and a pair of superb sidekicks: Paul Bettany of “Master and Commander” and Sean Astin, who comes close to stealing “Return of the King” as the soulful Samwise.

But there are half a dozen extremely strong contenders who could end up with nods instead.

Among them: Ian McKellen (“Return of the King”), Japanese star Ken Watanabe (“The Last Samurai”), William H. Macy (“Seabiscuit”), Alec Baldwin (“The Cooler”), Djimon Honsou (“In America”) and Bill Nighy (“Love Actually”).

BEST SUPPORTING ACTRESS

The one to beat here is past nominee Renée Zellweger, who gives the performance of her career as a tough-talking drifter in “Cold Mountain.”

But she’s got tough competition from a pair of newcomers in a category that historically has been friendly to fresh talent: Iranian actress Shoreh Aghdashloo, unforgettable as Ben Kingsley’s doomed wife in “House of Sand and Fog,” and 18-year-old Hollywood “It” girl Scarlett Johansson, who is being pushed as Best Actress for “Girl With the Pearl Earring” but is far more likely to score a supporting nomination for her delicate work as an adrift twentysomething in “Lost in Translation.”

And then there is 12-year-old Keisha-Castle Hughes of New Zealand, who enthralled audiences as the would-be tribal chieftain of “Whale Rider.”

The big question is whether Academy voters will go along with Newmarket’s risky strategy of gerrymandering her into the supporting category for what’s very clearly a leading role so she doesn’t have to face adults in the Best Actress race.

The fifth slot most likely will go to past nominee Samantha Morton, as an Irish immigrant in “In America.”

Also possible: Marcia Gay Harden (“Mystic River”), Melissa Leo (“21 Grams”), Holly Hunter (“Thirteen”), Hope Davis (“American Splendor”), Maggie Gyllenhaal (“Mona Lisa Smile”), Emma Thompson (“Love Actually”), Julie Walters (“Calendar Girls”) and Miranda Otto (“Return of the King”).