/sede/ of an organization is the place where the organization stays,
it could mean the building or the street address, depending
upon the context.
For some organizations, usually for very big ones, you also distinguish between
/sede operativa/ and /sede amministrativa/, or other kinds.
If you add 'di' (which in these cases is almost always implicit), it should be
clear:
sede operativa del servizio sociale territoriale.
sede: nome
operativa: aggettivo (from where operations start)
del : of the
servizio sociale: social service
territoriale: agg.: in the territory (local to the region, 'comune', 'provincia', whatever ...)