A brand of Bach that is rarely encountered came to the Kennedy Center last night when Helmut Rilling conducted the Gaechinger Kantorei of Stuttgart and the Los Angeles Chamber Orchestra in the B Minor Mass.

Early in the course of the music Rilling's overview of the masterwork became apparent.Every tempo stemmed both from the deepest meaning of the text and from the nature of the music, at the same time that all of the separate movements of the Mass, with their contrasting paces and moods, were being prepared to take their places in the vast mosaic.

If the opening Kyrie was taken with extreme deliberation, it was laid out in a way that revealed the total beauty of its long architectural lines. Choral ornaments were placed as expertly by the chorus as by the excellent soloists. The singing of the Kantorei has a special flavor not known in any other chorus. Five or six of the chorus members sang without scores throughout the long work. Each section is filled with a beauty of sound that changes from episode to episode, taking its character from the words at hand.

If the sopranos were marvels in the fleet lines of the fugal "et in terra pax ," whose tessitura held no problems for them, they were immediately answered in equal brilliance by their colleagues. Every note was impeccably placed in a technical display that is more often thought the province of the finest instrumentalists. Articulation was flawless even in the rapid tempos of the triumphant fugues.

Where Bach's music danced, Rilling's approach was altered to suit the mood. Where the central mysteries of Bach's faith were proclaimed, his direction opened great vistas of belief. One striking tribute to the performance came at the intermission when, in an unprecedented demonstration, the audience refused to let the performers leave the stage until a prolonged ovation finally ended.

The fine quartet of soloists included soprano Edith Wiens, contralto Margaret Cable, tenor Jon Humphrey, and bass Douglas Lawrence, each of whom added particular beauties. Humphrey, facing the fearsome demands of the "Benedictus," sang with a virile sweetness of rarest beauty. The Los Angeles Chamber Orchestra proved a marvelous ensemble, while its solo violin, flutes, three trumpets and horn were outstanding. It is possible to conceive of the B Minor being done differently than Rilling presented it. It is hard to think of it sounding better.

One minor question kept arising: Why use a portative organ that offered no bass underpinning in the many large passages of the Mass? There was often a feeling that an essential foundation was lacking. But this diminished in the face of Rilling's brilliant accomplishment.