Briefly covet short story about strong guys in green (13)
I believe the answer is:
environmental
'guys in green' is the definition.
'environmental' can be an answer for 'green' (I've seen this before). I'm not sure about the 'guys in' bit.
'briefly covet short story about strong' is the wordplay.
'briefly' means to remove the last letter.
'covet' becomes 'envy' (I've seen this before).
'short story' becomes 'mental' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'about' is a charade indicator (letters next to each other).
'strong' becomes 'iron' (iron can mean strong or powerful).
'envy' with its last letter taken off is 'env'.
'mental' put after 'iron' is 'ironmental'.
'env'+'ironmental'='ENVIRONMENTAL'
(Other definitions for environmental that I've seen before include "To do with one's surroundings" , "Pertaining to the surrounding world" , "Green" .)