Something's killing the new Superman movie -- and it isn't a load of kryptonite.

On Monday, Brendan Fraser and soap star Matthew Bomer became the latest to flee the high-profile movie project faster than a speeding bullet. Their departure followed the exit last week of Paul Walker of The Fast and the Furious fame, while studio honchos were still smarting over rejections by Josh Hartnett, Jude Law and Ashton Kutcher.

Now, Warner Bros. has to decide whether to dump director Brett Ratner, whose option to direct the trilogy expired on Saturday.

Ratner -- the third director on the project after Tim Burton and then McG (Charlie's Angels) dropped out -- is rumored to have clashed heatedly with producer Jon Peters over the glacial pace of casting.

"Brett probably has one idea and the studio has another," says casting director Matthew Barry, who has worked with Ratner on Family Man, Rush Hour and Rush Hour 2.

"Brett is very, very, very selective. When I worked with him on those three films, we had to scour the earth to find the perfect person for every role, not just the leads."

Barry says that while he admires Ratner's skills as a filmmaker, he can see his refusal to budge from his own vision causing friction with the studio.

"'Difficult' is the wrong word," Barry says, "but would I work with him again? They'd have to pay me a lot of money."

Warner Bros. yesterday declined to comment on whether it would renew Ratner's option or scout for another director, and Ratner's rep didn't return a call seeking comment.

Hollywood insiders point to the 10-year commitment required to film the projected trilogy -- and the inevitable typecasting -- as major stumbling blocks to finding an actor willing to don the cape and blue spandex.

"Christopher Reeve came from a soap and the theater, and [after Superman] he could never really break into doing just regular movies," says casting director Roger Mussenden, who adds he had to work hard to get actors to commit to two X-Men movies.

Comic-book fans would welcome a changing of the guard.

"We don't want to see Brett Ratner do this," says Gerry Gladston, owner of Manhattan's biggest comic-book store, Midtown Comics.

"You need someone known to be able to pull off a great adventure yarn, whether it's a superhero movie or not. You want someone to do for Superman what Sam Raimi did for Spider-Man -- that's the new benchmark."

But Chris Mason, co-founder of the Web site superherohype.com, says fans are worried the Superman movie will never see the light of day if Ratner departs. "It's beginning to look like this movie's never going to happen," he says.

The tortured casting process of Superman is becoming a running gag in Hollywood, and some observers even cite superstitions about "The Curse of Superman" as a factor.

They note that Reeve was paralyzed in a 1995 horseback riding accident; Margot Kidder, who played Lois Lane, suffered a nervous breakdown in 1996; Richard Pryor, who was in Superman III, was struck by multiple sclerosis; and TV Superman George Reeves was found dead of a single gunshot wound to the head in 1959.

But 80-year-old Marvel comics creator, the legendary Stan Lee, says he can't imagine why actors -- particularly less established stars -- would balk at the role.

"I would take the role myself if I were younger!" Lee told The Post. "It seems to me it's certainly going to be a big movie and could make somebody a very big star."

The bottom line from the fan boys and girls: Just get on with it, already.

"There's a whole new generation just champing at the bit to see a Superman film," Gladston says.