I know that there are several levels of security in the US Gov't. By Bush being president, I was wondering if he has the power to access any facility (Military, NASA, CIA, NSA,FBI) or any other organization at any given time without giving a reason for his inspection?

I would think so, all of these agencies are part of the executive branch of government and he is the boss of every executive office. Some are created by congress, but he still is the boss.

Yes, but he still has to knock before entering a ladies restroom.