Last night's choral concert by the Ron Freeman Chorale in the National Gallery was an unsettling affair, once the opening unaccompained Mass by Lassus was over. In that work, the "Missa Bell' Amfitrit' Altera," the chorale sang with generally good intonation, failing in pitch only in some passages late in the "Credo."

One of the great problems for today's choral conductors is the secret of maintaining the proper flow in extended works of Renaissance polyphony like the Lassus. Freeman began very well, but before the work was ended, had come out with some rather square passages that went too much beat by beat.

Troubles began to multiply in Monteverdi's Mass for Four Voices, chiefly because of the misguided use of trombones in support of the voices. Monteverdi wrote each of his Masses for unaccompained chorus, but indicated in each that the organ might be added. In only two or three passages of an earlier Mass than last night's he used trombones or violas. The presence of the trombones last night made any feeling of legato impossible, and, in such passages as the "Hosanna," became ridiculous.

Zoltan Kodaly's Missa Brevis was given its U.S. premiere in this city more than 30 years ago, with the composer conducting the choir and soloists of the National Presbyterian Church, while its organist, Theodore Schaefer, played the organ accompaniment. That was an occasion still remembered by many in this city.

For all its simplicity of style, it is a very difficult work for any chorus, thanks to its particular harmonic idiom and the extremes of range in all four voices.

Last night it was plagued by an electronic organ that ruled out any hope of a proper sound, and that, unfortunately, seemed to make it difficult for the singers to stay on pitch, for the intonaion at times approached the excruciating. Under the circumstances, it would have been better to omit the "Ite Missa Est," the vocal parts of which were added by the composer in a moment of creative weakness. But this is music that can be of overwhelming beauty. Last night it had little chance.