We have seen the past of rock & roll, and its name is BRITISH SEA POWER. And this, we can't emphasize enough, is a good thing, as evinced on their debut album, THE DECLINE OF BRITISH SEA POWER (Rough Trade), a pitch-black-perfect channeling of such gloomsters as the Smiths, Joy Division, and the Cure. Depressing ditties like ''Fear of Drowning'' (''...and all the money in the world/Won't help you now'') are sure to put a frown on even the most well-adjusted mope-rockers. But it's not all darkness: The Brighton, England-based quintet offers enough straight-ahead rockers to keep the CD from turning into dirge overkill. In fact, the track-4-and-5 combo that yokes the yearning splendor of ''Something Wicked'' to the fist-pumping fury of ''Remember Me'' gets our early vote for the best back-to-back song pairing of the year. The only decline we expect from British Sea Power is in their undeserved obscurity.