Blue Berets are defending Washington in the dark (7)
I believe the answer is:
unaware
'in the dark' is the definition.
(I've seen this before)
'blue berets are defending washington' is the wordplay.
'blue berets' becomes 'UN' (United Nations peacekeepers).
'defending' is an insertion indicator (inserted letters are defended).
'washington' becomes 'wa' (two letter abbreviation for the state).
'are' placed around 'wa' is 'aware'.
'un'+'aware'='UNAWARE'
(Other definitions for unaware that I've seen before include "Without knowledge" , "Uninformed" , "Ignorant - unenlightened" , "Not knowing (of a situation or fact)" , "Nescient" .)