The term "policy" can mean many things to many people. There are agency policies, county policies, state policies, and national policies that determine what social services are offered and who might get those services. The funding for social services is a hodgepodge of federal, state, and private funding, which makes policy and services a complex issue.
Generally, social services funded by the federal government through the state government provide for a "floor" of requirements that reflect policy, and the state is free to offer more, often with some sort of "ceiling" of its own.
Social policy is theoretically reflected in the guidelines set by the federal or state government. For example, if guidelines for cash assistance or food stamps did not provide more help for more than two children, we could infer that there was a social policy agenda that sought to deter having more children. Similarly, programs that provide assistance for a limited period of time reflect a social agenda of promoting the work ethic. How income guidelines are set demonstrates our societal willingness or unwillingness to help those in need.
Agencies that are privately funded are free to set their own policies, which reflect the missions and agendas of those who fund the agencies. This creates difficulties quite often when such agencies provide social services in other countries, for example, those that have set up shop in Haiti and other third world countries. Their agendas and policies do not necessarily reflect the agendas and policies of a host country. Another example is the missionary agency that does social work, promoting a pro-life agenda and refusing to provide birth control services.
Social work and social services are broad categories, including everything from food stamps to provision for an elderly person leaving the hospital. Policy certainly controls what services are provided and who gets them, but it is difficult, if not impossible, to generalize.