Ron Paul is not a pacifist. He is believes in the Christian Just War Theory and believes in the US Constitution. If you believe in these two things then you must only support war if it is being fought in defence, if the fight is proportional to the attack, if no other means of solving the conflict are possibile. And the Constitution says that war must be declared, and that it can only be declared by Congress.
But no, Ron Paul is not a pacifist.