Seventeenth-century Venice, the Venice of Monteverdi's day, was a center of commerce and diplomacy. It was wealthy.It was grand. The doge and his court proceeded, wherever they went, amid a riot of splendor and pomp, and at the heart of all this stood St. Mark's Cathedral.

Last night the glories that ennobled St. Mark's during the Christmas season resounded, again, about the National Shrine of the Immaculate Conception, where guest conductor Denis Stevens led the shrine choir in a performance of Monteverdi's newly resurrected Christmas Vespers.

Stevens, who is an English musicologist and conductor, is the world's leading authority on Monteverdi. What he has done here is to piece together, primarily from two collections of Vesper odds and ends, a complete and coherent service for the Christmas festival.

In so doing, he has had to write in missing vocal parts (missing due to printing mishaps) reconstruct the orchestration (here realized for strings, trombones and organ) and complete several of the sections. The result is stunning.

At the shrine last night, the work appeared in the complete context of chanted antiphons and prayers. These were intoned from the back of the nave by the shrine's Schola Cantorum. In front, the shrine's superb 24-voice choir and orchestra were entrusted with the concerted body of the psalms and canticles that make up the vesper service.

Soloists from the choir negotiated the virtuosic melismas of Monteverdi's word painting with distinction. The choir itself sang with unfailing beauty and a thorough understanding of the difficult stylistic touches that characterize all of Monteverdi's music.

This ease and familiarity with the idiom is Stevens' work, no doubt. But the remarkable vocal accuracy, absolute pitch perfection and choral balance are a testimony to the training and leadership of choirmaster Robert Shafer, who, last night, was continuo organist.

In an interview earlier in the week, Stevens indicated that the shrine's acoustics would pose no problem. In this he was overly optimistic. Although the sound was much better than it has been in the past, words were still largely inaudible -- all the words, that is, except for those of cantor Patrick Jacobson, whose marvelous diction survived even those obstacles.

This first American performance of the Christmas Vespers is a major musical event, and it got the sort of performance it deserved. The concert will be repeated tonight.