If they "bust" into your house, I hope you're wearing "Depends". The element of surprise is what makes these raids so successful. They will most likely have you eating carpet chunks before you could reach for any firearm.
The first thing a legitimate team will do, besides knocking your door off the hinges, is to identify themselves and order everyone inside to "freeze"! Even if they've made a mistake (which doesn't happen very often), you are far better off being calm and collected. Ask to see their warrant. Do what they say.
Chances are if such an event did occur, as they entered your house and saw you (the intended perp) reaching for a gun, you'd be in pretty deep doo-doo.
On the other hand, if you hear that these types of raids are being carried out regularly by men in black ninja suits and MP5's against law abiding folks for no other reason than to violate your rights, then by all means do what you need to do. But the odds will be stacked against you unless you regularly wear body armor and a gas mask while lying in bed, holding onto a switch to some Claymores.
Stay out of trouble, and just don't worry so much. Otherwise, you may be just a bit paranoid.
My guess is that we are a long way (in this country) from what you are worrying about.