Samuel W. Lewis, a former U.S. ambassador to Israel, had a key negotiating role in the Camp David peace talks in 1978 during the Carter administration. (Courtesy of the U.S. Institute of Peace)

Samuel W. Lewis, a career diplomat who was the U.S. ambassador to Israel for eight years and who had a major role in negotiating the Camp David peace talks in 1978 that resulted in a historic treaty between Egypt and Israel, died March 10 at his home in McLean, Va. He was 83.

The cause was lung cancer, said his son, Richard Lewis.

Mr. Lewis held several top-level diplomatic positions through his three-decade career with the State Department but none so sensitive as his tenure in Israel, where he served as ambassador from 1977 to 1985. He was present in 1977 when Egyptian President Anwar Sadat became the first Arab leader to visit Israel, opening the door to a future agreement.

The Camp David negotiations between Sadat and Israeli Prime Minister Menachem Begin took place under the guidance of President Jimmy Carter, Secretary of State Cyrus R. Vance and national security adviser Zbigniew Brzezinski. Mr. Lewis revealed some of the critical steps in the talks in a 1998 oral history for the Association for Diplomatic Studies and Training.

“The conference went on for days and days,” Mr. Lewis said, “as did the tennis games, the walks in the woods, the meals, the pool games, the drafts, the meetings.”

He also noted that Carter’s team viewed Begin with wariness, considering the recently elected Israeli leader a confrontational hard-liner.

“There was one event that occurred that I remember still vividly,” Mr. Lewis said in the oral history. “As Carter left the cabin to return to his own, he asked me to walk with him. He said in a very frustrated and angry manner: ‘I don’t think Begin wants peace. He really doesn’t.’ I told him that he was wrong, that Begin and all Israelis wanted peace above all. They had been wanting nothing else for years.”

Mr. Lewis, who knew of Begin’s long history of personal struggles, first in Poland and later in Israel, recommended a more nuanced approach — what he later called “honey before vinegar.” He shuttled between Begin and Carter, conveying new developments in the negotiations.

“Sam set a frame of reference that allowed Carter to understand Begin,” Aaron David Miller, a vice president of the Wilson Center and a former U.S. Middle East negotiator, said Wednesday in an interview. “He managed to gain Begin’s confidence and that set the stage for what I think is the most important act of diplomacy by an American president ever in the Middle East.”

The Camp David Accords were signed Sept. 17, 1978, and within months Begin and Sadat were jointly awarded the Nobel Peace Prize. A formal treaty between Egypt and Israel was announced the next year, calling for Israel to withdraw its forces from the Sinai Peninsula and placing limits on Egypt’s military presence in the region.

“Nothing was more important than this heroic act of diplomacy,” Miller said. “There was a time when American ambassadors had the will, skill and power to make a difference in diplomacy. Sam was, bar none, one of the best.”

Samuel Winfield Lewis Jr. was born Oct. 1, 1930, in Houston, where his father was a salesman.

He became interested in foreign affairs at Yale University, from which he graduated in 1952. He received a master’s degree in 1954 from Johns Hopkins University’s School of Advanced International Studies and then began his Foreign Service career.

He had early diplomatic assignments in Italy and Brazil, and served on the National Security Council in the late 1960s. He was in Afghanistan from 1972 to 1974 and was acting ambassador in 1973 when a coup deposed the country’s king.

Mr. Lewis later served as a top State Department planning official and as an assistant secretary of state before going to Israel. His most trying times as ambassador came after Israeli forces launched an attack on Lebanon in 1982, creating turmoil in the Middle East and fraying Israel’s relations with the United States.

During that time, Mr. Lewis was often berated in scathing one-on-one sessions with Begin over U.S. policy toward Israel.

“I’ve seen better political theater before,” Mr. Lewis quipped to The Washington Post in 1982, “but not to such a small audience.”

Mr. Lewis left Israel in 1985 and later spent six years as president of the U.S. Institute of Peace, an independent, federally funded agency that seeks to resolve international disputes without violence. He was the State Department’s director of policy planning in 1993 and 1994 in the Clinton administration, taught at Georgetown and Johns Hopkins universities, and was an adviser to foreign-policy think tanks concerned with settling disputes between Israel and the Palestinians.

Survivors include his wife of 61 years, Sallie Smoot Lewis of McLean; and two children, Grace Lewis of Oakton, Va., and Richard Lewis of McLean.

Mr. Lewis was in frequent demand as a commentator on conflicts in the Middle East and was considered one of the foremost diplomatic experts on U.S.-Israeli relations.

“We are really irrevocably bound to each other and entangled in a whole variety of ways,” he told The Post in 1985, “and it is in the nature almost of a family relationship.”