A US president accepted war to be advanced (7)
I believe the answer is:
forward
'be advanced' is the definition.
(synonyms)
'a us president accepted war' is the wordplay.
'a us president' becomes 'ford' (Gerald Ford).
'accepted' is an insertion indicator.
'ford' going around 'war' is 'FORWARD'.
'to' acts as a link.
(Other definitions for forward that I've seen before include "going on" , "advance" , "team player" , "Fresh" , "Promote" .)