federal agency vs bureau

federal agency and bureau both are nouns.

Word	Noun	Adjective	Verb	Adverb
federal agency	Yes	No	No	No
bureau	Yes	No	No	No

As nouns, federal agency and bureau are synonyms defined as:

Other synonyms of federal agency include agency, authority, government agency, office.

federal agency (noun)	bureau (noun)
an administrative unit of government	furniture with drawers for keeping clothes
	an administrative unit of government