The melodic opulence of the Brahms piano quintet is accessible to all the major chamber ensembles that frequent our concert stages, but the secrets of the extended passages that bridge these gorgeous melodic structures remain elusive to most. The members of the Emerson String Quartet, together with pianist Lambert Orkis, have solved these mysteries by treating whole sequences of long Brahms phrases as single units with their own internal shape, structure and direction. Thus, at their concert at the Smithsonian's Baird Auditorium Saturday, the middle of the second movement Andante took on a dynamic energy-building role, and the finale built to a powerful and unrelenting conclusion.

Orkis, who is among today's finest and most musical of chamber musicians, led the ensemble in this process of exploration and discovery, searching for a sense of rhythmic inevitability that succeeded everywhere except in the thematic statement of the second movement. Here he delayed the second note of the melody every time it occurred, an idea that would have worked if the piano were capable of real voice leading.

The Emerson's rise to preeminence among chamber groups can perhaps be accounted for by its understanding of the ways that music moves and by its ability to allow time to unfold at its own subjective pace. It was this command over time that gave the opening Brahms clarinet quintet such a palette of moods. The midsection of the second movement was allowed to gather itself together decisively, the third movement proceeded with a sunny leisure and the finale danced with a marvelous Viennese flavor. Clarinetist Loren Kitt, who seemed a little reticent at the beginning, quickly moved into the balanced partnership that allowed his beautifully shaped playing to be fully effective.