Robert Shafer conducted the Oratorio Society in a vigorous, precise account of Mozart's Requiem at the Kennedy Center last night and paired that lofty creation, in hopelessly invidious comparison, with a "Grand Mass in D" by Antonio Salieri.

Of course, it was Salieri who, legend has it, poisoned Mozart in a snit of peer-jealousy, killing him and leaving the Mozart Requiem unfinished. When Peter Shaffer expropriated this tale for the plot of "Amadeus" he tossed out the murder thesis but also socked Salieri and his work an esthetic black eye.

One side effect of the play, though, has been to make Salieri a familiar name for the first time in about a century and a half. And a few of his works are being heard again, even if only as curiosities. Last night's Mass was a sort of pocket-mass; it lasted about 20 minutes, was in five parts and was too brief to develop much sense of spiritual majesty.

The materials were not strong enough to do that anyway, regardless of the proportions. There was no sense of daring, but the ideas were at least respectable, with the exception of one blundering modulation in the "Gloria" just before a solo cello passage that a competent high school dance band would have avoided.

Being juxtaposed with the Mozart Requiem might be a little hard on anyone, especially when sung and played with such discipline. The choir was in particularly splendid shape. In the "Rex tremendae" that opening word was shouted out with an exactitude that only a very well rehearsed group could repeatedly do. The soloists were good, especially soprano Elizabeth Knighton and tenor Stanley Cornett.