Questionable American Pastor infiltrating religious group (7)
I believe the answer is:
suspect
'questionable' is the definition.
(similar in meaning)
'american pastor infiltrating religious group' is the wordplay.
'american' becomes 'US' (abbreviation for United States).
'pastor' becomes 'p' (abbreviation).
'infiltrating' indicates putting letters inside.
'religious group' becomes 'sect' (eg a religious sect).
'us'+'p'='usp'
'usp' inserted inside 'sect' is 'SUSPECT'.
(Other definitions for suspect that I've seen before include "Imagine to be guilty" , "Presume" , "One thought to have committed crime" , "Dubious" , "Be ready to believe - one of the usual crowd?" .)