By DAVID GERMAIN

LOS ANGELES — James Cameron’s science-fiction epic “Avatar” had another stellar weekend with $68.3 million domestically, shooting past $1 billion worldwide, only the fifth movie ever to hit that mark.

No. 1 for the third-straight weekend, 20th Century Fox’s “Avatar” raised its domestic total to $352.1 million after just 17 days. The film added $133 million overseas to lift its international haul to $670 million, for a worldwide gross of $1.02 billion.

“Avatar” opened two weekends earlier with $77 million, a strong start but far below dozens of other blockbusters that debuted as high as $158 million. But business for other blockbusters usually tumbles in following weekends, while “Avatar” revenues barely dropped over the busy Christmas and New Year’s weekends.

“It’s like a runaway freight train. It just keeps doing business,” said Fox distribution executive Bert Livingston. “Here’s what’s happening: I think everybody has to see ‘Avatar’ once. Even people who don’t normally go to the movies, they’ve heard about it and are saying, ‘I have to see it.’ Then there’s those people seeing it multiple times.”

“Avatar” was Cameron’s first film since 1997’s “Titanic,” the biggest modern blockbuster with $1.8 billion worldwide.

Cameron now is the only filmmaker to direct two movies that have topped $1 billion. Along with “Titanic,” the others are “The Lord of the Rings: The Return of the King” at $1.13 billion, “Pirates of the Caribbean: Dead Man’s Chest” at $1.06 billion and “The Dark Knight” at a fraction over $1 billion, according to box-office tracker Hollywood.com.

With “Avatar” closing in on No. 2 film “The Return of the King,” Cameron is in striking distance of having the two top-grossing movies globally.

“Avatar” has had a price advantage over those other billion-dollar movies. About 75 percent of its domestic business has come from theaters showing it in digital 3-D presentation, those tickets typically costing a few dollars more than admissions for the 2-D version.

Finishing at No. 2 for the weekend was Robert Downey Jr.’s crime caper “Sherlock Holmes” with $38.4 million. The Warner Bros. film lifted its domestic total to $140.7 million after 10 days in theaters.

In third place was 20th Century Fox’s family tale “Alvin and the Chipmunks: The Squeakquel” with $36.6 million. It raised its 10-day total to $157.3 million.

The top-three movies, along with solid holdovers that included Universal’s “It’s Complicated” at No. 4 with $18.7 million, steered Hollywood to a big start to 2010 after a year of record revenue.

Hollywood finished 2009 with $10.6 billion domestically, easily surpassing the previous record of $9.7 billion in 2007, according to Hollywood.com.

Factoring in today’s higher admission prices, the year was strong but not a modern record-breaker for number of tickets sold. According to Hollywood.com, domestic admissions came in at 1.42 billion in 2009, the most in the last five years, though well below the modern record of 1.6 billion in 2002.

In Hollywood’s glory years of the 1930s and ’40s, before television eroded the movie audience, estimated movie attendance ran as high as 4 billion some years.

Studios began 2010 with a headstart over last year. Overall revenues came in at $230 million, up 50 percent from New Year’s weekend in 2009, when “Marley & Me” was No. 1 with $24.3 million.

Like “Titanic” 12 years ago, “Avatar” has fairly clear sailing now that the holidays are over. Hollywood is entering a slow season, when fewer big movies arrive and competition is lighter.

“Titanic” lingered as the No. 1 film for months leading up to the Academy Awards, where it won 11 Oscars, including best picture and director.

“Avatar” also proved a critical favorite with strong Oscar potential. Cameron broke new ground in combining live-action, digitally-enhanced performances, visual effects and 3-D presentation to immerse viewers in his futuristic tale of humans and aliens on a distant moon.

“Leave it to James Cameron to do this. To not only set the technical world on fire, the visual world on fire, but also the box-office world on fire 12 years after ‘Titanic,”’ said Paul Dergarabedian, box-office analyst for Hollywood.com.

Estimated ticket sales for Friday through Sunday at U.S. and Canadian theaters, according to Hollywood.com. Final figures will be released Monday.

1. “Avatar,” $68.3 million.

2. “Sherlock Holmes,” $38.4 million.

3. “Alvin and the Chipmunks: The Squeakquel,” $36.6 million.

4. “It’s Complicated,” $18.7 million.

5. “The Blind Side,” $12.7 million.

6. “Up in the Air,” $11.4 million.

7. “The Princess and the Frog,” $10 million.

8. “Did You Hear About the Morgans?”, $5.2 million.

9. “Nine,” $4.3 million.

10. “Invictus,” $4.1 million.