I second all lincolnsgrandson's answers, but will go a bit further w/ the last question.
Clerkship are absolutely not included in any loan forgiveness program. Many, if not all, firms will give you "firm credit" for a clerkship (you'd start as a 2nd year associate) and give you a sizable bonus. Your clerkship brings prestige to the firm, so you are rewarded for making crap money for another year or two.
The DA might be included in the program. From what I've heard, most loan repayment programs require non-private jobs where you are making less than $50k or something. Whether governmental jobs (DA, Pub. defender, etc.) count will depend on the school and their individual programs.