They say that breaking up is hard to do, but for bands, the really hard part is staying together. Witness Natural Bridge, a fusion-oriented quintet calling it quits after 3 1/2 years with a blowout finale at the Bayou tomorrow night. Originally formed by members of Tim Eyermann's East Coast Offering, Natural Bridge grew into a top-notch original band known for its frequent collaborations with dancer-choreographer Carla Perlo and her company.

"The business just wasn't supporting us," says keyboard player Gregg Karukas. The local club scene kept shrinking and though the group did well on the college concert circuit, "we weren't making enough money to stay together full time and we couldn't do the music we were doing just by being a weekend band." When bassist Mike Manring decided to move to New York for further study, guitarist Gerry Kunkel decided to spend more time with his family, and "the rest of us can't afford to stay together," Karukas says.

A year and a half ago, several major labels expressed strong interest in Natural Bridge, which had been circulating a tape produced at the local Omega Studio. "It just got strung out, so we decided to put it out ourselves." Because of the cost, they put out "Free Sample" as a tape instead of an album (a practice copied locally by the traditional Southern Comfort Band and internationally by former Washington black punksters, the Bad Brains).

"It's ironic that the tape is being accepted so well now," says Karukas, who will work in a jazz trio format and may move to the West Coast next fall. "It's time for everybody to change, to move on and do other things." Percussionist Steve Bloom will continue his collaborations with Perlo. And, with an eye to future music archivism, tomorrow's Bayou performance will be videotaped.