OK i found the way, i am looking for it since yesterday. Of course I've ran the game first.
The solution: http://modsreloaded.com/camera-zoom download from the link the .zip and paste the .ini file in the ini folder that you have to make in the data folder (because there is no ini folder in generals). It works perfect
I haven't tried GenTool because i found that it gives you the control of the zoom level only during replays and not live in the mission.