Exactly. You need to keep your "cardio" workouts [u]short and intense[/u] in order to get all the benefits without losing muscle mass or strength.
It's the sprinter vs. marathon runner analogy. Read some of Ross Enamait's stuff (his books are great). He has some incredibly tough conditioning circuits that are short (20-30 minutes or less) but extremely intense. They will get you in shape, help you get leaner and help you keep your muscle and strength.
Renegade Training and Joe DeFranco follow similar ideas/methods.