What is ActionScript
The mobile applications developed using FlashLite 1.0 and 1.1 uses ActionScript 1.0 only.
From FlashLite 2.0, the ActionScript 2.0 language can be used for mobile application development.
in 2006 ActionsScript 3.0 was released with Flash 9. It is a big refurbishment of the language, using a different virtual machine. The virtual machine for the older versions of ActionScript is included for compatibility. 3.0 is considered a significant performance booster and entails a more robust model.
Currently there is no FlashLite version which supports ActionScript 3.0
Read more about ActionScript on Adobe's developer site