If Pretty Girls Make Graves’ third album, “Elan Vital,” is any indication, the band’s fourth album will be either an instant classic, or their worst and probably last album. “Elan Vital” finds the band exploring new waters, but far too hesitantly. Alternately promising and disappointing, the album displays musical growth but at times fails to transcend the most superficial level of that growth to become an exciting album in its own right. On “Elan Vital,” Pretty Girls Make Graves are often treading water; only their next album will decisively indicate whether the band will sink or swim.

The band’s most obvious change is the exponential increase in musical color. The addition of Hint Hint’s Leona Marrs on keyboard is the most dramatic addition, particularly noticeable on the driving “Pyrite Pedestal.” But other touches throughout the album — in particular the Gogol Bordello-esque accordian (also courtesy newcomer Marrs) on the bizarrely proggy sea-shanty “Selling the Wind” — indicate the band’s departure from the sound of their previous albums, 2003’s “The New Romance” and 2002’s “Good Health.”

This is not to say that the New York-style post-rock (as opposed to the more ambient post-rock of Chicago bands like Tortoise) of “The New Romance” is completely absent. Nick Dewitt’s complicated yet not overdone drumming complements the echoing electric guitar and background shouts that channel Les Savy Fav in opener “The Nocturnal House.”

But the band elsewhere sidesteps, at least partially, their math-rock past. “The Number,” a much more straightforward rock song, owes more to fellow Washington natives Sleater-Kinney than to any post-rock forbears (and not merely thanks to Andrea Zollo’s vocals). Derek Fudesco’s fierce bass in particular evokes Corin Tucker’s down-tuned guitar, even as it guides the song’s frenetic tambourine and percussive keys. A change in production probably helped the band along here; previous producer Phil Ek, famous for the post-rock sound of his work with Les Savy Fav and Modest Mouse among others, has been replaced by relative newcomer Colin Stewart (whose previous producing credits include P:ano and They Shoot Horses, Don’t They). Guitarist J Clark also lends substantial production assistance.

The lyrics are thankfully less maudlin than on past Pretty Girls Make Graves releases (though a Smiths reference as a band name was always somewhat of a warning in that regard). Yet they are hardly inspiring. The extended anthropomorphic metaphor in “Magic Hour” is beyond tiresome; the music, a dull match, resembles Franz Ferdinand (with whom Pretty Girls Make Graves recently toured). But even that pales in comparison to the song’s positively awful concluding couplet “Open up your eyes / This hate’s eating me alive.” And the odd working-class anthem “Parade” calls for “Strike!” and “Mutiny!” for the workers from “the fields and the factory lines” but, like a Le Tigre song minus the message, fails to explain what, exactly, the song’s subjects are fighting for.

This uncertainty is exemplary of the album as a whole. The band flirts with different styles easily but without the commitment necessary to sell the songs. Pretty Girls Make Graves possesses startling technical proficiency, and further, they avoid the boastfulness that often accompanies such skill. Yet much of “Elan Vital” sounds frustratingly like a confused band in a fitting room.

The most notable, and refreshing, exception is the one-two love-song punch of closing tracks “Wildcat” and “Bullet Charm.” Anchored by Derek Fudesco’s Sonic Youth-inspired bass line, the succinctly beautiful “Wildcat” showcases stunning work from all band members. Marrs’ lilting keyboard and Clark’s guitar tussle over on-point percussion from Dewitt, as Zollo’s distinct and powerful vocals all but chant the abstract lyrics, excellent save for the cliched last line “Love is eternal.” All this in just over three minutes — a surprising feat for the usually five-minute-per-track Pretty Girls Make Graves.

“Bullet Charm,” on the other hand, is as similar to the band’s past work as anything on “Elan Vital,” plus it’s head and shoulders above their work on “The New Romance.” Sentimental but not overly so, the lyrics shine thanks to sweetly charming delivery from Zollo (backed up by Marrs). Meanwhile, like a wannabe Dave Newfeld, J Clark smartly wrangles bird-call trumpet (recorded at his house), string samples and intricate drum-machine percussion into a thing of simple Pro Tools beauty.

That the album concludes so strongly bodes well for the band’s future efforts. But the spotty energy on the whole is frankly troubling. “Elan Vital” presents two roads for the band: toward an unprecedented masterpiece or towards mediocrity and obscurity. If the band takes the former road, it will be hard to begrudge them the growing pains exhibited here. But no matter what the result, “Elan Vital” itself will fail to be essential listening.