You can only get into drdo provided you have done your bachelor's  from IIT OR NIT , as they recruit only from IIT'S AND NIT'S . You must be at that top level so that they can recruite you without Mtech . You must have done some kind of research or major projects . 

It is difficult to get into drdo without Mtech . It is better to do Mtech and then get into drdo as you may have better chances of selection.