Opera houses are always keeping their repertories alive by giving us new productions of old favorites, and that is what the National Symphony has done this year with its annual oratorio, "Messiah." It opened last night and was a triumph.

In place of the rather solemn Big Chorus "Messiah" tradition typical of the NSO, this new one is characterized by grace and light.

What conductor Gerard Schwarz has done is restore "Messiah" roughly to the limited balance of forces available to Handel on that April 13, 1742, in Dublin at the first performance. J. Reilly Lewis' Washington Bach Consort Chorus numbered about 45. And the NSO was reduced to even a smaller size. But counting the four soloists as well, there were considerably fewer persons on the Kennedy Center Concert Hall stage than in a normal "Messiah" chorus.

When the singers and players are this skilled it is amazing what such a combination of forces does for the balances and transparent tones of the music. The chorus, especially, had a crispness and spring to its work that you don't usually hear in "Messiah." And if the truth be known, their enunciation was actually better than that of any of the four soloists, fine as they were.

There was no more striking example than the mighty final chorus, starting "Worthy is the Lamb that was slain," and ending with repeated mixtures of the other vocal lines with repeated assertions of "Amen," even though "Messiah" is not a liturgical work. It seemed clear as crystal, and had great spirit. Heresy it may be, but "Messiah" just was never meant for the Mormon Tabernacle choirs of the world.

Likewise the orchestra had no problem being heard over the chorus. Once again textures were light, with real buoyancy. And for once that Elysian moment, the brief Pastoral Symphony, was genuinely soft.

Obviously, such a fine "Messiah" is not just a result of good balances, though. Lewis and Schwarz, who run the Los Angeles Chamber Orchestra as well as New York's Y Chamber Symphony, share a view of "Messiah" in accord with contemporary notions of proper baroque performance practice. Still, to contradict a popular misconception, this does not lead to pedantic playing; quite the contrary.

At the first chorus, "And the glory of the Lord shall be revealed," the lightness and clarity was already shining through. And throughout the evening choral, attacks and releases were wonderfully precise and decisive.

The spirit of all this often charged the fine soloists. Tenor Rockwell Blake, for instance, has a small voice that he sometimes pushes too hard in 19th-century music. But not here. Starting from his initial "Comfort ye," his coloratura runs were splendidly even and his tone lovely.

Soprano Phyllis Bryn-Julson and mezzo Beverly Wolff were in fine form, and never more so than in that stunning melody that comes near the end of the first part, "He shall feed His flock," which the mezzo sings first and which is then picked up by the soprano. It occurred to one that if only Bryn-Julson's strong, ringing highs and Wolff's rich lows could be combined in one voice, it would really be something.

Baritone Jan Opalach got off to a slow start but was singing well by the time he got to "The trumpet shall sound."

This exhilarating version of one of music's most popular works will be repeated tonight, tomorrow, Saturday and Sunday.