Oh! I didn't know they are confusing.They do not mean the same. I'm not even sure what they are supposed to mean.
It's difficult to say how they are different when they are not even common collocations.
Where did you find these phrases?
Rover
OK-ishBNC lists it, but at no. 287 in the 'public + <noun>' possibilities - more than 130 times less common than 'public sector' (the commonest in BNC - not in COCA though). See more here: corpus.byu.edu/bnc/x.asp?
Given the context, it would be possible to work out what 'public issue' signifies, but I think a native speaker would use more words - something like 'issue of popular/current concern'. Are you trying to do a word-for-word translation of two words in your native language, azhu?
'Agenda' comes from the Latin agenda, meaning 'things that should be done'. In its concrete form an agenda is a list of things to be discussed at a meeting. However, 'agenda' can have a figurative meaning - 'things that someone wants to do'. This explains the collocation 'public agenda': 'things that someone wants done, made public'. This is probably the usage your friend heard..
b
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