Messiahs come and Messiahs go. This may not be sound theologically, but it is a seasonal, Handelian fact, and, as Messiahs go, the Nationl Symphony's performance at the Kennedy Center last night went very well.

Robert Shafer, who is a model of clarity on the podium, molded a performance to his exacting specifications. It was characterized, first of all, by precision and confidence. Its baroque idiom was intelligently adapted to concert hall-sized forces. Its dispassionate non-romantic approach emphasized the glories of the purely musical aspect of this work which, often, is obscured in the dramatization. And even the orchestra sounded thoroughly rehearsed.

One hundred and fifty strong, the Oratorio Society of Washington moved with impressive agility and unanimity that belied their size, but managed this without any of the annoying choral tricks often used to achieve these virtues.

The soloists seemed to revel in the opulence of truly Handelian ornamentation.

Tenor Rockwell Blake set the tone with a smashing performance of "Every Valley," flexible, accurate and full of splendid ornamentation. None of the others was quite able to match this, but contralto Lili Chookasian and bass Thomas Paul did nice, business-like and musical jobs.

Soprano Susan Davenny Wyner made nice sounds but much of what she said was unintelligible and many of her lines wobbled and whooped out of focus.

Ornamentation, which often is relegated to a few desultory, self-conscious vocal cadences, delightfully found its way into the instrumental parts also in this performance, from whence they emerged with fresh and welcome elegance.