government agency vs office

government agency and office both are nouns.

Word	Noun	Adjective	Verb	Adverb
government agency	Yes	No	No	No
office	Yes	No	No	No

As nouns, government agency and office are synonyms defined as:

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

government agency (noun)	office (noun)
an administrative unit of government	a religious rite or service prescribed by ecclesiastical authorities
	the actions and activities assigned to or required or expected of a person or group
	a job in an organization
	place of business where professional or clerical duties are performed
	professional or clerical workers in an office
	an administrative unit of government
	(of a government or government official) holding an office means being in power