What do you mean by "support"? Apple lately offers security update for the current OS and the 2 previous. In the past it had been current and 1 previous. There's no way of knowing what Apple's plans are.
Currently Apple supports Mountain Lion, Lion and Snow Leopard with software and security updates. I doubt it will change when Mavericks comes out, just Snow Leopard will be not supported and Lion will take it's place.