A handful of fair-to-good tunes (''She Used to Be Mine,'' ''House,'' ''Sister Sisyphus'') makes the Spin Doctors' third studio album, You've Got To Believe in Something, an improvement over their sophomore flop, Turn It Upside Down. Yet what comes through loudest is the sound of effort, a straining to recapture the electricity that seems, sadly, to have struck this band just once: on its quintuple-platinum '91 debut, Pocket Full of Kryptonite. At their best, the Spin Doctors play blue-eyed funk, with drummer Aaron Comess (one of the supplest in rock) and bassist Mark White laying down a diamond-hard, endlessly repeating groove the perfect foil for singer Chris Barron's airy improvisations. The tunes on Kryptonite that avoided this format were the least successful, and the same holds true on Believe. Problem is, most of the new songs avoid this format.
You can't blame the Spin Doctors for wanting to stretch, but they haven't found anything remotely as effective as the soul-funk of their early hits ''Little Miss Can't Be Wrong'' or ''Two Princes'' (though they do pull off a decent power ballad, ''She's Not You''). Their ordeal for what we seem to be witnessing is a band's protracted demise is as much a result of music-biz hype and expectations as anything else. A group of modestly talented guys (with the exception of Comess) hit on a nice little sound, build a following, get marketed furiously, and sell a billion records. Great things seem in store for them, but in the end they are what they are: a group of modestly talented guys. C+