Firstly it is a very good thought as you are thinking of helping the needy people.
But with or as a Civil service servant, you would e indirectly connected with the poor people. You would be more of a government servant and would serve the nation.
But in-case if you take up Sociology and are a Sociology Graduate followed by an MSW ( Masters in Social work), you would be dirctly working with social issues related to education, poverty, nutrition etc.
Another way is by being a Graduate and work in the corporate sector. Corporates are associated with CSR ( Corprorate Social Responsib