Records of leading US composer (8)
I believe the answer is:
archives
'records' is the definition.
(I've seen this before)
'leading us composer' is the wordplay.
'leading' becomes 'arch' (e.g. in arch-enemy).
'us composer' becomes 'ives' (I've seen this before).
'arch'+'ives'='ARCHIVES'
'of' is the link.
(Other definitions for archives that I've seen before include "Record collection" , "Official records" , "Rich vase (anag.)" , "Historical records of an institution" , "Chronicles" .)