An American diplomat enlisted by Democratic and Republican presidents to negotiate cold war treaties with the Soviet Union on nuclear weapons and human rights. Mr. Kampelman, who was a legislative counsel to Senator Hubert H. Humphrey of Minnesota in the 1950s, had become a prominent lawyer in Washington when he received a call from another Minnesotan, Vice President Walter F. Mondale, in 1980. President Jimmy Carter wanted Mr. Kampelman to represent the United States at the coming East-West meetings in Madrid, in which the United States was seeking to bring the Soviet Union and some Eastern European countries into compliance with world human rights accords signed in Helsinki, Finland, in 1975. Mr. Kampelman took the job reluctantly and only after being assured it would last just three months. Instead it lasted three years — deep into the first term of President Ronald Reagan, who retained Mr. Kampelman as lead negotiator. Less than two years later — even after Mr. Kampelman had served as an adviser to Mr. Mondale in his 1984 presidential campaign — President Reagan appointed him to lead arms-control talks with the Soviets in Geneva. Mr. Kampelman returned to his private law practice in 1989, but the negotiations eventually led to the 1991 Strategic Arms Reduction Treaty, reducing nuclear weapons. When Mikhail S. Gorbachev, the last president of the Soviet Union, toured the United States as a private citizen in May 1992, his schedule included a meeting with Mr. Kampelman. Mr. Kampelman also served as chairman of WETA, the public television station in Washington, and was a founder and moderator of “Washington Week in Review” (now “Washington Week”) on PBS. Mr. Kampelman graduated from New York University in 1940 and enrolled in law school in the university’s night program soon afterward, working to support himself during the day. Mr. Kampelman opposed Communism as a young man, but he also opposed war, and he requested conscientious objector status during World War II. He was eventually sent to the University of Minnesota, where he was one of 36 volunteers who served in an experiment to study the effects of severe weight loss through what essentially was controlled starvation. Even as Mr. Kampelman’s weight fell to 100 pounds, he continued to study toward his law degree at N.Y.U., which he received in 1945. He later received master’s and doctoral degrees in political science from the University of Minnesota. Mr. Kampelman began working as a Humphrey aide when he was mayor of Minneapolis in the 1940s and later joined his Senate staff. His political views underwent a transformation along the way: he went from being a declared pacifist to a centrist regarded as a hawk by left-leaning Democrats. In addition to his son, he is survived by two daughters, Julia Stevenson and Sarah Kampelman, and five grandchildren. His wife, the former Marjorie Buetow, died in 2007; the couple were married for 58 years. A son, David, died in 2004, and a daughter, Anne Wiederkehr, died in 2006.