By outsourcing do you mean that you are working in the Central government Office but your salary is paid by another person, agency, legally referred to as Contractor?
Or is it that the government is paying you salary directly but your terms of appointment is that you are hired for a fixed term, say 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 who pays you salary to give you leave (with salary) and to substitute another employee of your skill to do the work in the government office who is the principal employer.
In the second case, the government order appointing you would say that you are hired on a daily wage basis and as such you will be paid only for the days you are present and there is no leave applicable. In another term it s called "exploitation". It is interesting that the government is the law enforcing authority and the same government is responsible to ensure that employees are not being exploited and they are paid statutory minimum wages, they are given leaves as per law, they are not compelled to work more than 8 hours etc etc. But they themselves have highly paid officers and sub officers who will not do any work but they can engage people like you to do their work for which these benefits are not applicable. Sorry to say that this happens only in India....!!