The song by Jerry Herman is "Avenue A," which is the street where Mrs. Santa Claus (played by Angela Lansbury) ends up on her trip around the world, when her sleigh develops some sort of sleigh trouble (hopefully it was under warranty), and she has to set down. No one there knows who she is, just a friendly stranger, but she's welcomed to the mixed-culture neighborhood in turn-of-the-century New York City.
The number is sung by David Norona, with Debra Wiseman as his unrequited beloved Sadie trying to promote women's rights. (Afterwards, there are a couple of poster-edited cuts that jump to two brief reprises.) By the way, keep an eye out at the 2:35 mark for a brief cameo by composer Jerry Herman playing the piano is an 1890s mustache.