First, the birth of Christ, which probably took place in 6 B. C., in a cave not a wooden structure, and not on December 25 Then, a smooth tracing of Christmas customs from pre-Christian festivals to Rudolph the red-nosed reindeer. Covering the usual topics--tree, food, music, gifts, etc.--Stevens links medieval and later customs with earlier pre-Christian practices and shows how other traditions have arisen or been modified in the New World. She cites various possible origins for St. Nicholas, for whom ""legends are plentiful but facts are few,"" and she doesn't give undue attention to other, still-prevalent legends such as that of Martin Luther and the Christmas tree. (Detroiters, however, might well resent her crediting Macy's-New York as the first Thanksgiving Day Christmas parade.) A seasonal stand-by.