Hi Himanshu,

If you had checked the officially issued list of upsc cse optional subjects then you will find out that there are 25 optional subjects from which we can choose irrespective of your ug/pg specialised subjects.

In that list the optional subject no.21 is of 'public administration'.

And,as this comprehensive source of public administration you are talking about is in actual the part of the subject public administration, so you can easily opt for this subject( public administration ) as you optional subject choice for upsc cse.

Good luck.