Game offered by leading Italian agent (1-3)
I believe the answer is:
i-spy
'game' is the definition.
'leading italian agent' is the subsidiary indication.
'leading' says to take the initial letters.
'agent' becomes 'spy' (spy is a kind of agent).
The initial letter of 'italian' is 'i'.
'i'+'spy'='ispy'
'offered by' is the link.
(Other definitions for i-spy that I've seen before include "Child's game: ''. ... with my little eye'" , "Children's alphabet game" , ". ... with my little eye (children's game)" , "Game played with young children" , "Wordgame" .)