* "G.I. Joe" earns $100 million worldwide
* Costly action film leads N.America with $56.2 million
* "Julie & Julia" cooks up $20.1 million
(new throughout, recasts lead; adds quotes, analysis)
LOS ANGELES, Aug 9 (Reuters) - A new action movie based on the "G.I. Joe" line of toy soldiers crushed enemy forces at the worldwide box office during the weekend, ending the three-week reign of the sixth "Harry Potter" fantasy.
"G.I. Joe: The Rise of Cobra" sold about $100.3 million worth of tickets, distributor Paramount Pictures said on Sunday.
The three-day take of $56.2 million from the United States and Canada ranks as the fourth-highest August opening ever, and comes after the $175 million effects extravaganza had been besieged by bad buzz for months.
The foreign component of $44.1 million -- from 35 markets comprising 75 percent of international sales -- was led by South Korea ($5.6 million). The film opened at No. 1 in two countries not exactly favorable to American militarism, China ($4.8 million) and Russia ($4.6 million).
"Harry Potter and the Half-Blood Prince" earned $31 million worldwide, taking its total to $816 million. The North American total of $274 million was bolstered by a fourth-place $8.9 million weekend. The film was released by Warner Bros. Pictures, a unit of Time Warner Inc (TWX.N).
Besides "G.I. Joe," other new entries in North America included Columbia Pictures' Meryl Streep culinary offering "Julie & Julia" at No. 2 with a tasty $20.1 million, and indie producer Relativity Media's horror-thriller "A Perfect Getaway" at No. 7 with just $5.8 million.
Last weekend's North American champion, the Adam Sandler comedy "Funny People," slid to No. 5 with $7.9 million, taking the 10-day total for the $75 million comedy to a disappointing $40.4 million. The film was released by Universal Pictures, a unit of General Electric Co (GE.N).
"G.I. Joe" stars Channing Tatum and Marlon Wayans as two young soldiers recruited by the international G.I. Joe military force to help save the world. It was directed by Stephen Sommers of "The Mummy" fame.
While based on the venerable Hasbro Inc HAS.N action figures, the film tips its hat to the multilateral series of dolls relaunched in the 1980s rather than the American-oriented military heroes coveted by boys in the 1960s and 1970s. (G.I. is a generic term for U.S. soldiers.)
Given the wide awareness of the brand, fans were underwhelmed by a trailer that premiered in February during the Super Bowl football championship, the most-watched television event of the year in the United States.
Paramount opted not to screen the movie in advance for critics, a gambit often reserved for box office clunkers. In the end, reviews were predictably bad but not as bad as those for such recent releases as "G-Force" and "The Ugly Truth."
"I think it plays to real people," said Don Harris, executive vice president of distribution at the Viacom Inc VIAb.N-owned studio. "They check their disbelief at the door and have a good time with the movie."
Surveys indicated the film played best in the American heartland -- anywhere "east of Beverly Hills and west of Manhattan island," Harris said. It also was especially popular with Hispanic and black moviegoers, he said.
Overall, male moviegoers accounted for 60 percent of the audience, with an even split either side of 25 years.
Based on the film's better-than-expected $22 million opening on Friday, Paramount had forecast a $60 million weekend. But Saturday sales fell more steeply than expected. Harris said he was not troubled by the decline.
The record for an August opening was set in 2007 by "The Bourne Ultimatum" with $69.3 million, while "Rush Hour 2" kicked off with $67.4 million in 2001, and "Signs" with $60 million in 2002. All ended up with more than $220 million.
Columbia Pictures offered some effective counter-programming with "Julie & Julia," which pulled in older women. Streep plays Julia Child, while Amy Adams stars in a parallel story as a young woman who seeks to replicate the noted TV chef's culinary exploits.
He expected the $38 million film, which was directed by Nora Ephron ("Sleepless in Seattle"), to simmer in theaters for some time. (Writing and reporting by Dean Goodman; Editing by Bill Trott)