A port is a place where ships load and unload; a harbor is a body of water providing protection for ships. Although the terms are somewhat loosely used interchangeably, port applies particularly to the town or city, including its commercial aspects, that provides a harbor: "New York is a great port city with an excellent harbor." Both port and harbor have a meaning of "haven," a place of comfort, rest, and security: "any old port in a storm"; "a harbor for weary travelers."
Dictionary of problem words and expressions. Harry Shaw. 1975.