I m fresh graduate and also I have associate engineering diploma, please guide me that either I should go on office administration side or engineering side?

Engineering side, of course. It is much more interensting.

Later you'll always have time for administration.

ENGINEERING SIDE , IF YOU START WITH SITE ENGINEER , YOU WILL GET TO MOST INFORMATION THAT U WILL NEED LATER IN DESIGN OR OTHER DEPARTMENTS 

Depends on the area of that you choose to gear up your career.

If you have good practical experience, then you must consider the engineering side but if you are more comfortable in handling the situations from the back end, then prefer going at the administration side. 

If you want expertise yourself in both ways then I suggest engineering side. Later on you can try for admin activities.