Eighteenth-century Germany knew how to celebrate Christmas. The holiday went on for 12 days, and there was music for every minute. That tradition has been lost around here, where carols and other Christmas music disappear, as if by decree, at the stroke of 12 on Christmas night.

It was a particular pleasure therefore to have the Washington Bach Consort, under the direction of Reilly Lewis, prolong the season with a performance of Bach's "Christmas Oratorio" at the National Presbyterian Church Saturday.

Bach intended the six cantatas that comprise his oratorio to be performed serially on Dec. 25, 26 and 27 and on three other festivals, culminating with the Feast of the Epiphany on Jan. 6, the 12th day of Christmas. But like the ghosts of Christmas Past, Present and Future, Reilly Lewis did it all in one day, taking time out in the middle for a dinner break.

Lewis' forces have improved enormously over the past several years. He now has a chorus of 45 singers who blend beautifully, who are well balanced and, above all, who can negotiate Bach's instrumental vocal lines with agility, accuracy and clarity. His splendid instrumentalists boast solo strength and fine ensemble. And his vocal soloists sing with a thorough idiomatic command of the music.

All of these elements were evident in this performance. After an opening chorus that was a hair too slow, Lewis found ideal tempos for the rest, moving with alacrity but without haste.

Organ interludes between cantatas were nicely handled by Albert Wagner.