Hi Soma,
I had replied without reading your further input, by seeing your further input it seems that you requried to configure input service tax where part of the service tax you pay to vendor and part will be paid to goverment.
In this case you will requried to set you tax procedure with two type of condition type one will be service tax credit - billed (which you have paid to vendor) and another with unbilled (which is liability). Please find below snap of the tax procedure.
hope this will help you.
Thanks,