These days, we don't ask a whole lot from Britney Spears as an entertainer. She can bungle her dancing, muss her weave, and sleepwalk through a video (like the flatline clip for first single ''Hold It Against Me''), and we'll still send her straight up the charts simply because she's Britney. Because we were there in 1998 when she first bare-midriffed her way into the zeitgeist, and we were there a decade later when she lost her way and, for a brief time, custody of her two children. She's an American institution, as deeply sacred and messed up as pro wrestling or the filibuster.
Musically, though, Spears will always have to measure up to her own gold standards of pop euphony: the operatic slither of 2004's ''Toxic'' and the candied funk of 2000's ''Oops!...I Did It Again.'' Femme Fatale, her seventh studio LP, has moments that meet that challenge. Molded by all-star helmers Max Martin and Dr. Luke (the guys behind Katy Perry, Taio Cruz, and just about every song you've karaoked in the past year), the album is a ballad-free, treadmill-ready playlist of tireless dance beats and top-shelf production. At its best, it's an undemanding ride through the marvels of modern-day electro-pop, from the dubby grind of ''Inside Out'' to the giddy sing-along of second single ''Till the World Ends'' (sample lyric: ''Oh-oh-oh-oh-oh-oh-oh-oh-oooh''). But Brit wobbles when she gives in to her old penchant for music-box melodies (the treacly ''Trip to Your Heart'') or tries to play an ersatz Fergie on the will.i.am-produced romp ''Big Fat Bass.''
Femme Fatale can also be jarring on a lyrical level. Judging by surveillance records from the tabloid panopticon, Spears is a workaday mom who likes buying off the sale rack at Walmart and going to Little League games with her kids. Judging by these songs, she's a childless man-eater who could drink Ke$ha under the table. That disconnect, added to the fact that Spears doesn't claim so much as a co-writing credit on a single track, can make the album feel like an autopilot affair.
Still, Britney always brings one undervalued asset to the table: her reedy, preshrunk voice probably the single most maligned instrument in music this side of the vuvuzela. Spears is no technical singer, that's for sure. But backed by Martin and Dr. Luke's wall of pound, her vocals melt into a mix of babytalk coo and coital panting that is, in its own overprocessed way, just as iconic and propulsive as Michael Jackson's yips or Eminem's snarls. No matter who she might be outside the studio, the Britney we hear on Femme Fatale is a confidently corrupt guide to a place where our only worry is whether the beats will end before the sun comes up. And when it comes to pop stars, what more can we really ask for? B+