William G. Clark will replace Peter A. Langerman as director of the New Jersey Division of Investment, Trenton, effective March 12, said Orin Kramer, chairman of the state's Investment Council. Mr. Clark was appointed by state Treasurer John McCormac and was recommended by the council. Mr. Clark is deputy director of the division, which oversees the state's $67.1 billion pension fund. Mr. Langerman announced his resignation in January. Messrs. Langerman and Clark were out of their offices and not available for comment. Information on Mr. Clark's replacement was not available by press time.