The post-entertainment embassy bash following a performance at, say, the Kennedy Center is a standard Washington social ritual. The French have done it. The Germans have done it. This fall the Austrians are going to do it. And, in the past, even the Chinese have done it.

Last night, though, the Colombians decided to return that ritual to hallowed convention -- the centuries old custom of presenting the recital on the premises and having the social hours (in this case, a black-tie buffet) as an afterthought. In effect, it was the old-fashioned musicale. So as such an expert as Arts Endowment Chairman Livingston Biddle could recall, this is not the way it has been done here, normal as it might seem.

Ambassador and Mrs. Virgilio Barco had good reason to break the pattern, for they had visiting with them Colombia's most famous musician, harpsichordist Rafael Puyana. Still in his 40s, Puyana is one of that legion of baroque authorities who have restored their subtle, understated instrument to its pre-piano position as the proper keyboard instrument for Bach and Handel, Scarlatti and Soler and countless others before Mozart and Beethoven came along along.

Thanks to recordings Puyana is fairly well known, even though his performances here have been relatively few. After he studied in the United States with that High Priestess of the Harpsichord, Wanda Landowska his career developed mostly in Europe. And he came for the Colombian Embassy event directly from his home in Paris.

"You have to understand that when we were all growing up together," said Mrs. Barco, "there really wasn't that much musical tradition in Colombia. But Rafael was very determined, even from his youth. So he came to the United States for his training.

"Then after the years passed, we were assigned to Washington, and at that time Rafael said that he would come here to visit, and to play. And this is it." As the ambassador explained to the audience of several hundred, Puyana "came for the sole purpose of playing for friends in Washington."

Impresario Patrick Hayes said that if Puyana were playing for pay, there is little doubt that the audience would have been considerably larger, given the performer's reputation.

But it also would have been in a larger hall. And the delicate sounds that were so well attuned to the acoustics of the embassy's elaborately molded early 20th-century ballroom might have been lost,

The first half of the program was one of the milestones of the keyboard repertory, Bach's D-major partita. Then there were Spanish baroque works keyed to today's Columbus Day celebrations (the Latin countries still do it on the right day). The recital was clearly one of the outstanding performances of the week in this city.