In the '50s, rock 'n' roll was pure and simple. In the '70s, rock has become an umbrella term that shelters diverse explorations into musical genres. Spawned by the art-conscious sensibility of the later Beatles, the '70s has been the decade of fusion music. Pursued by the likes of Kansas, Genesis, ELO and Renaissance, progressive/art rock with classical overtones has been one manifestation of fusion music.

Saturday night at the Merriweather Post Pavillion, Kansas once again demonstrated that rock can be loud yet precise, energetic yet sophisticated. They also reaffirmed a basic conflict of art rock: descipline versus inspiration. The danger is that replacing the energy and authenticity characteristic of good rock with complex orchestrations screens and dilutes the central force.

Those numbers where the fusion worked such as "The Wall," "Portrait" or "Bringing It Back," revealed a new facet of a many-faceted gem. But where it didn't work the tone appeared clouded and cluttered with imperfections - the orchestration itself being one of the obfuscating factors. At times like these, fusion is more like being caught between a rock and a hard place.

Opening for Kansas was DFK ("We're not really a band, we're running for president"), a new association for the artists Les Dudek, Mike Finnigan and Jim Krueger, all of whom have solo albums on Columbia.

Asked at 7 p.m. to go on a half-hour earlier than scheduled and given no opportunity for a sound check, the new band did not play under the best of circumstances. The little I heard (I arrived for the scheduled 8 p.m. start) was loud and distorted.