What I found as the most effective way to do this is via a
ketogenic diet. There is a great book called the Art
and Science of Nutritional Ketosis, by Dr Phinney and Dr Volek. There are a lot of free youtube videos by both doctors Phinney and Volek who describe how to lose fat, while protecting and building physical and athletic strength. Really good stuff.
So, through proper nutrition, you can lose the fat and maintain/build muscle.
Hope this helps. Good luck!!