Morton H. Halperin (born June 13, 1933) is an American expert on foreign policy and a minor figure in the scandals of the Nixon administration known as Watergate being listed on Nixon's Enemies List.

Halperin served in the Department of Defense in the 1960s and was dovish on the Vietnam War, calling for a halt to bombing Vietnam. When Nixon became president in 1969, Henry Kissinger, his new National Security Advisor announced Halperin would join the staff of the National Security Council. The appointment of Halperin, a colleague of Kissinger's at Harvard University in the 1950s, was immediately criticized by General Earle G. Wheeler, chairman of the Joint Chiefs of Staff; FBI director J. Edgar Hoover; and Senator Barry Goldwater.

Kissinger soon lost faith in Halperin. A front page story in The New York Times on May 9, 1969, stated the United States had been bombing Cambodia, a neutral country. Kissinger immediately called Hoover to find out who might have leaked this information to the press. Hoover suggested Halperin and Kissinger agreed that was likely. That very day, the FBI began tapping Halperin's phones at Kissinger's direction. (Kissinger says nothing of this in his memoirs and mentions Halperin in passing about four times.) Halperin left the NSC in August 1969 after only seven months but the tapping continued until February 1971.

He was a friend of Daniel Ellsberg. When Ellsberg was investigated in connection with the Pentagon Papers, suspicion fell on Halperin, who some Nixon aides believed had kept classified documents when he left government service. John Dean claimed that Jack Caulfield had told him of a plan to fire-bomb the Brookings Institution, Halperin's employer, to destroy Halperin's files.

The tapping of Halperin's phone was not revealed until 1973, when it came out in Ellsberg's trial. He sued Nixon and won a symbolic $5 judgement in 1977 for the offense.

In 1985 he won a MacArthur Foundation fellowship.