Over a three-decade career, Mr. Bartholomew held high-level positions within the Defense Department, the National Security Council and the State Department. In the late 1970s, he was a key negotiator in the second round of strategic arms limitation talks between the United States and the Soviet Union, known as SALT II.
He navigated the thorny issues related to U.S. military bases in countries that included Somalia and Greece and the U.S. deployment of weapons in Europe. Later, as American interests in Europe expanded beyond security, Mr. Bartholomew schooled himself in economics and served as ambassador to Spain and Italy.
Leslie Gelb, a former colleague and president emeritus of the Council on Foreign Relations, described Mr. Bartholomew as one of the premier American diplomats in Europe for many years.
"Very few people will just come at foreign leaders as hard as he did and as effectively as he did," Gelb said in an interview. Military bases, in particular, were a sensitive issue because they symbolized U.S. power over a region. Mr. Bartholomew was adept at persuading leaders abroad to help maintain a U.S. presence in the face of strong internal political opposition. "That's an art," said Gelb.
Mr. Bartholomew's most visible public role came as ambassador to Lebanon from 1983 to 1986. He arrived in the country one day before the truck bombing on Oct. 23, 1983, that killed 241 people at a Marine barracks in Beirut.
Less than a year later, Mr. Bartholomew was wounded in a bombing of the U.S. Embassy in East Beirut that killed more than a dozen people. He had to be pulled from the rubble.
"God knows, it was bad enough, but it could have been a hell of a lot worse," he said at the time. Had the truck been closer to the embassy when the bomb detonated, the casualties could have been higher, he added.
Mr. Bartholomew traveled in a bulletproof limousine, which at times came under fire, and was accompanied by at least 10 bodyguards. His residence in Lebanon was attacked, his wife said.
In the aftermath of the bombing of the Marine barracks, Gelb said, Mr. Bartholomew was one of the first policymakers to argue against the immediate withdrawal of troops. In his view, pulling out would be bending to terrorists' demands.
Mr. Bartholomew was described in news account as one of the last "holdouts" when President Ronald Reagan in February 1984 ordered U.S. ground troops to leave Lebanese soil.
In June 1985, Mr. Bartholomew worked for weeks to help secure the release of dozens of American hostages after Islamic extremists hijacked TWA Flight 847 from Athens to Rome.
Mr. Bartholomew left Beirut in 1986 and began a three-year stint as ambassador to Spain. He later served as undersecretary of state for arms control and international security affairs and as U.S. permanent representative on the NATO council.
In the mid-1990s, he served as a special envoy to Bosnia in an early effort to end violence in what had been Yugoslavia. The fighting ultimately ended with the 1995 Dayton peace accords, of which Richard C. Holbrooke was the principal architect.
After completing a four-year ambassadorship in Italy in 1997, Mr. Bartholomew remained in the country for a number of years as a top executive with the international offices of Merrill Lynch. He retired in 2011.
Reginald Bartholomew was born Feb. 17, 1936, in Portland, Maine. He received a bachelor's degree in history and political science from Dartmouth College in 1958 and a master's degree in political science from the University of Chicago.
Early in his career, he taught social sciences and government at the University of Chicago and Wesleyan University in Middletown, Conn.
Mr. Bartholomew began his government work in the late 1960s at the Defense Department, where he became known as a top authority on European security issues.
He moved to the State Department in 1974 and rose through the ranks, including an assignment on the National Security Council. He later was assistant secretary of state for political-military affairs, a top position in the State Department. During his years in Washington, he lived in the Hollin Hills neighborhood of Alexandria and in Georgetown.
Survivors include his wife of 56 years, Rose-Anne Dognin Bartholomew of New York City; four children, Sylvie Bartholomew of Springfield, Christian Bartholomew of Bethesda, Damien Bartholomew of Annandale and Jonathan Bartholomew of London; a brother; and seven grandchildren.
Mr. Bartholomew, who was described as the consummate diplomat, immersed himself in local customs. While ambassador to Spain, Gelb said, Mr. Bartholomew once hosted a party at his residence and impressed his guests by taking to the stage and stamping his feet in a flamenco dance.