Underage Eminem fans are using every trick in the book to sneak into the red-hot rapper's new R-rated flick -- and driving theater owners nuts.

Desperate to see 8 Mile, kids are waving fake IDs, trying to bribe ushers, sneaking in without tickets and begging older strangers to act as their guardians, managers at Manhattan movie houses said yesterday.

"They try everything. The security guards really have their hands full this week," said an assistant boss at the Union Square Stadium 14, who declined to give his name.

To see the acclaimed hip-hop drama -- which contains nonstop cursing, sex scenes, violence and drug use -- kids are supposed to be at least 17, or be accompanied by a parent or a guardian over 21.

But that didn't stop Scott Gallie and Maria Evans, two high school freshmen, who scammed one New York City theater.

"They wouldn't let us buy tickets for 8 Mile, so we just got tickets for I Spy, then snuck in," said the 14-year-old Gallie.

Added Evans, also 14: "We just had to make sure the movie was on the same floor as 8 Mile."

Terrence McKenzie, an 18-year-old high school senior, acted as the guardian for his 16-year-old school chums, Tom Tucker and Eric Eve -- and had no problem getting in.

"I love Eminem and just had to see the movie," Eve said.

At some theaters eagle-eyed ushers set up checkpoints to examine IDs.

"If you don't catch them at the box office, then you catch them when you take their tickets," explained a manager.

But how much trouble can theaters really get into? Not much.

Theaters are under no legal obligation to enforce the ratings system, created in 1968 as a guide for parents, and can't get into hot water if they don't.

"There's no tooth of law behind it. It's a voluntary system, and whether it's enforced is totally up to each theater," said Rich Taylor of the Academy of Motion Picture Arts & Sciences, which created the ratings system.

Last night, the Parents Television Council, a watchdog group, asked theaters across the nation be extra tough, after its spot checkers found many letting kids as young as 14 in without a hassle.

8 Mile raked in $54.5 million over the weekend, mostly from teens and 20-somethings.

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