Generation X has always seemed the embodiment of Groucho Marx's dictum about not wanting to be a member of any club that would have you. That goes double for Stephen Malkmus, Gen X's aging slacker princeling.

As leader of Pavement, Malkmus spent the better part of the '90s zigging whenever his fan base zagged, and the better part of the last decade cranking out the kind of Aspergerian solo records that scare off women and try men's souls.

While the pretty, wryly observed pop songs of his latest, Mirror Traffic, mark a welcome return to effortless likability, his performance with the Jicks at the TLA Wednesday night was another matter altogether.

Things started off promisingly. The Jicks sounded taut and well-oiled, and Malkmus' guitar-playing blazed brightly on a trifecta of songs from the new album - the bell-bottomed breakup blues of "All Over Gently," the spastic congressional comeuppance of "Senator," and the weary-boned windout of "Brain Gallop."

Despite his 45 years, Malkmus still looked the lanky undergrad - with his boychick bangs, lived-in jeans, adidas World Cup kicks, and well-worn Times New Viking T-shirt - striking bold, air-quote-free rock poses.

But four songs later he seemed to lose interest, tossing off the vocal to "No One Is as I Be" like an old gum wrapper. "Church on White," a choice cut from his 2001 solo debut, also suffered from uninterested singing, as did "Spazz," which otherwise lived up to its title, with the Jicks remaining in the pocket despite the song's disorienting time-signature shifts.

Malkmus seemed to reengage on the middle-age miasma of "Share the Red" and the head-bobbing zoom of "Discretion Grove," as well as the pretty persuasion of "Asking Price" - only to wave goodbye and exit stage right.

But by the second song of the encore, "Jenny and the Ess-Dog" - arguably his most perfect pop song - it became apparent that Malkmus' indifferent vocals were less a matter of the spirit being unwilling than the flesh being weak. Perhaps he had a cold or his voice was simply tour-ravaged, or maybe he just can't hit those sighing high notes the way he used to, but whatever the cause, Malkmus was clearly struggling to get through what should have been a victory lap.

Closing with a hoarse, whispered "Fall Away" - the kind of song cool parents sing their kids to sleep with - Malkmus sent us out into the humid South Street night with the nagging sense that we had not quite gotten our money's worth.