Seventeen-year-old actress Britney Spears couldn't land more than a role in an off-Broadway update of The Bad Seed until she scored a contract with the Backstreet Boys' record company. She was flown to Sweden's Cherion Studios, the Lolita-pop doll house where 'N Sync, Robyn, Five, Ace of Base and the Backstreeters all record their Eurofied impersonations of teen-targeted American R&B. Spear's theatrical experience has paid off: The Swedish-designed dance grooves of her slinky, S&M-tinged smash, ". . . Baby One More Time,"recall the glory days of S-S-S-Samantha Fox, effectively transforming this ex-Mouseketeer born in a tiny Louisiana town into a growling jailbait dynamo. Yet the ballads of her debut evoke the worst of Debbie Gibson, even as Spears mimics the mannerisms of her hero Mariah Carey. While several Cherion-crafted kiddie-funk jams serve up beefy hooks, shameless schlock slowies, like "E-Mail My Heart," are pure spam.