TRADITIONAL ASIAN DANCE companies are no longer such rare breeds. Some of them, like Gamelan Sekar Jaya and Chitresh Das Dance Company, are even locally grown. However, dances from Thailand, be they contemporary or traditional, are still quite rare. That's why the appearance of the 13-member Royal Thai Ballet – brought to San Francisco in conjunction with the Asian Art Museum exhibit "The Kingdom of Siam: The Art of Central Thailand, 1350-1800" – is such a welcome opportunity to see how the Buddhist country interprets Hindu mythology. The Royal Thai Ballet is bringing a lavishly costumed type of dance drama known as "khon." Traditionally performed by men (and noblemen, to boot), khon is loosely related to India's kathakali, and uses spectacular masks and costumes and elaborate mudras (codified gestures) to reenact stories from the Ramayana. You will encounter gracefully floating heroes and heroines, crudely stomping demons, and everyone's favorite: the monkey king, who always falls on his feet while trying to negotiate the treacherous terrain between gods and humans. 7 p.m., 401 Van Ness, S.F. $19-$39. (415) 392-4400. (Rita Felciano)