BACH: Mass in B minor. Sylvia McNair, Delores Ziegler, sopranos; John Aler, tenor; Thomas Paul, bass; Atlanta Symphony Orchestra and Chamber Chorus, Robert Shaw conducting. Telarc CD-80233 (two CDs).

BACH: Mass in B minor. Jennifer Smith, soprano; Michael Chance, countertenor; Nico van der Meel, tenor; Harry van der Kamp, bass; Netherlands Chamber Choir, Orchestra of the 18th Century, Frans Bruggen conducting. Philips 426238-2 (two CDs).In the Mass in B minor, which Johann Sebastian Bach put together in 1747-48 (just two years before his death), he summed up his choral genius. For the resultant glorious pastiche, he drew upon a number of his previous compositions and added some new movements, thus creating a musical colossus that has survived 21/2 centuries, and seems likely to endure for another 250 years.

Ironically, neither means nor opportunity existed in Bach's day to give a full-fledged rendering of the work, so he never heard it complete during his lifetime. But in the interim the lack has been made up by thousands of performances, ranging from austere chamber forces to grandiose presentations by hundreds of choristers and instrumentalists, and Bach has proved durable enough to withstand all onslaughts.

As for the present instances, seldom have two recordings ended up so much in a dead heat for my preference. Both have persuasive elements to recommend them, and you would not go wrong with either.

Robert Shaw is a name that conjures the image of meticulous perfection, coupled with exquisite and often thrilling musicality. And notwithstanding the forces at his command, he has held his mass to a modest framework, using chamber chorus for flexibility, nuance and spirit, then letting out for the splendor and glory of a few great climaxes, complete with the peal of baroque trumpets and full orchestral support. As always, his tempos are ideal, his technical attention impeccable, and his understanding revelatory to the listener.

Bruggen has sought out original sources, including autographed scores wherever possible, for this recording; and while a complete tracing of the differences would require exhaustive study, the careful listener can detect a general air of greater simplicity and spareness in the music, enhanced by the original instruments of the orchestra.

Yet the music retains its splendor and sheen and its thrill in most respects, and Bruggen is also a sensitive conductor who well interprets the significance of the work. Only occasionally does one feel a certain tendency to mush along mechanically, clip-clipping off the beats - a feeling perhaps more attributable to the overpowering rhythmic dominance of the music than to a fault in the performance.

In both recordings the choruses are fine, and sing sensitively. Shaw commands the more assertive soloists with the more spectacular voices, including the laudable McNair and Ziegler, and tenor John Aler - a favorite of Shaw's for good reason, who sang in Salt Lake City with Shaw a few years ago when he conducted the Berlioz Requiem.

Bruggen's soloists are enjoyable, particularly soprano Jennifer Smith, though they are held to a narrower range dynamically and emotionally. Alto solos are assigned to counter-tenor, and while its use is authentically correct, the often straight sound does not completely convey the nuance requisite to an aria such as the "Qui sedes."