Lathem, who died Friday, was "a genuinely nice guy in a profession noted for its hard-bitten cynics," the Post said in an editorial.
He accompanied President Reagan on trips to the Soviet Union, China and West Germany, including the president's 1987 speech in Berlin when he urged Soviet leader Mikhail Gorbachev to "tear down this wall."
Lathem was also on the ground in Kosovo during the 1999 war, when he was serving as a Post Washington correspondent.
His beats included security affairs and intelligence, covering Osama bin Laden and international terrorism well before the Sept. 11, 2001, attacks on the World Trade Center and the Pentagon.
"He was a fine journalist and a treasured member of the staff," said Post Editor-in-Chief Col Allan. "He'll be sorely missed."
Lathem began his journalism career at New Jersey's Paterson News, joining the Post in 1980. After just three months at the Post's Manhattan headquarters, Lathem was promoted to Washington bureau chief.
Lathem spent five years, 1988-93, as White House correspondent for Fox News, before returning to the Post during the nascent days of the Clinton administration.
Lathem is survived by his wife, Ellen, a son and three sisters.
By: Niles Lathem, who spent much of the last three decades covering Washington and the world for the New York Post, has died of lung cancer at 51, the newspaper announced Saturday.