Hey Mithun.
If you're talking about applying for government jobs after completion of your BA LLB course then you will be able to apply for those where requirement in graduation. In case of law, post graduation will be completed after you have completed the coure of LLM. LLM is a course which is post graduation in law which is either for 1 year or for  years. Though it depends on which government job you are talking about. Because various government jobs related to law would require only LLB/ BA LLB as requirements.  Some might require  a several years of practice in court along. Some might require post grad or there might be extra weightage for post grad.
Best of luck