If the NA only appears in a field that is character anyway then there is no need to preprocess the file to remove them. They will not cause PROC IMPORT to define the variable with the wrong type. You can either leave the value as NA or convert it to blanks later if you want.
Ready to join fellow brilliant minds for the SAS Hackathon?
Build your skills. Make connections. Enjoy creative freedom. Maybe change the world. Registration is now open through August 30th. Visit the SAS Hackathon homepage.