They say two but if there is a huge demand for it they will make more than 2, also its not stated how many maps are per pack, what if they did something like 5 maps per pack, its all specualtion we wont know until the game comes out.
Side note: There is alot of shit that IW needs to fix from COD4, I can only stand to play this game for maybe and hour to an hour half before all the BS is to much.