''Sum of All Fears'' upsets ''Clones''

”Star Wars” didn’t even put up a fight.

Thanks to a troublesome third-week performance by ”Attack of the Clones,” Ben Affleck’s disaster drama ”The Sum of All Fears” handily topped the box office this weekend, earning a respectable $31.2 million, according to studio estimates.

The thriller, based on a Tom Clancy novel, features Affleck in the Jack Ryan role previously played by Alec Baldwin (”The Hunt for Red October”) and Harrison Ford (”Patriot Games,” ”Clear and Present Danger”). Since the film features a nuclear attack in the United States (specifically, at the Super Bowl in Baltimore), many analysts wondered whether movie audiences would want to see ”Sum” at this precarious point in our nation’s history. While the film’s opening can’t compare to those of recent summer hits like ”The Fast and the Furious” and ”Tomb Raider,” the $31.2 million take ranks as the best for a Clancy adaptation.

The big surprise of the weekend, however, is the poor performance of ”Star Wars: Episode II,” which fell a horrible 57 percent from the three-day portion of last week’s Memorial Day holiday to $20.7 for the weekend, bringing its three-week total to $232 million. By contrast, ”The Phantom Menace” grossed $32.9 million in its third weekend in 1999 and had reached $255 million at this point in its release. Although ”Clones” had a better opening weekend than ”Menace,” ”Episode II” will likely fall far short of ”Episode I”’s $431 million domestic total. Given fans and critics seem to prefer ”Clones” to ”Menace,” what explains the relatively poor performance? In a word: competition. Whereas ”The Phantom Menace” virtually had May and June to itself (the only other blockbuster in the summer of 1999 was ”The Sixth Sense,” which opened in August), ”Attack of the Clones” has had to contend with the much-loved ”Spider-Man.” In fact, Spidey’s box office supremacy will mean that ”Attack of the Clones” will be the first ”Star Wars” film not to be No. 1 for the year.

”Spider-Man,” meanwhile, managed to snag third place this weekend, grossing another $14.5 million and bringing its total up to $354 million. That’s $3 million short of the No. 5 film of all time, ”Jurassic Park.”

The weekend’s other new entry, the spy spoof ”Undercover Brother,” premiered with a nice $12.1 million — not a huge number but enough to top the $9.5 million debut of the first ”Austin Powers” flick. Can a sequel be far off?

And rounding out the top five was the animated film ”Spirit: Stallion of the Cimarron,” which, despite a 40 percent drop to $10.7 million, managed to beat Al Pacino’s well-reviewed ”Insomnia,” which fell a bewildering 53 percent to $9.8 million. The plummet can only be attributed to the beautiful weather much of the country experienced this weekend. Otherwise, director Christopher Nolan and company will have a tough time sleeping tonight after all.