By outsourcing, do you mean that you are working in the Central Government Office, but your salary is paid by another person or agency, legally referred to as a contractor? Or is it that the government is paying your salary directly, but your terms of appointment indicate that you are hired for a fixed term, such as one year, with some written terms and conditions of employment?
In the first case, it is the responsibility of the contractor, who is your employer and pays your salary, to provide you with leave (with salary) and to substitute another employee with similar skills to perform the work in the government office, who is the principal employer.
In the second case, the government order appointing you would state that you are hired on a daily wage basis and, therefore, you will be paid only for the days you are present, with no leave applicable. In other terms, this is called "exploitation." It is interesting that the government is the law-enforcing authority and is responsible for ensuring that employees are not exploited, are paid statutory minimum wages, given leaves as per the law, and not compelled to work more than 8 hours, etc. However, they have highly paid officers and sub-officers who do not perform any work but can engage individuals like you to do their work without these benefits. Unfortunately, this situation seems to occur only in India...!!