Service broadcast on behalf of church (3,5)
I believe the answer is:
air force
'service' is the definition.
(air force is a kind of service)
'broadcast on behalf of church' is the wordplay.
'broadcast' becomes 'air' ('air' can be a synonym of 'broadcast').
'on behalf of' becomes 'for' (I've seen this before).
'church' becomes 'ce' (abbreviation for Church of England).
'air'+'for'+'ce'='AIR FORCE'
(Other definitions for air force that I've seen before include "one of the services" , "Simple tune for church service" , "A country's flying service" , "Country's military planes" , "Kind of blue" .)