well some of you may be upset by this but bungie will impliment a new ranks system in the latest halo 3 title update. no announcement of when this starts but it will be soon.
First : NO your rank isnt getting reset.
Here is the simplest way i can explain it.
Your main service record will maintain your total xp and rank..always
each playlist will get its own military ranking, this is what will start new. so all of you say buh bye to your birdie. each playlist will start fresh with a recruit symbol, your xp and xp alone will change this, so each playlist will have its own military ranking but your skill rank (the number) will stay.
examples:
1. Social slayer : you will start off with recruit symbol and it wont display a numbered rank at all, as you get experience your rnak will increase up the symbol. But if you got to social big team after it will also start as a recruit symbol and so on. each playlist will have seperate ranks to show how much you play that playlist type.
2.ranked team: if you are a 45 now, you will start off as a level 45 recruit and have to build you military rank with exp.
its hard to explain, go to the latest bungie update for their explanation. http://www.bungie.net/News/content.aspx?type=topnews&cid=14994