Nathaniel Davis, 86, a longtime diplomat who was the American ambassador to Chile when President Salvador Allende was deposed in a bloody coup, died of cancer Monday in Claremont, Calif.

The death was announced by Harvey Mudd College in Claremont, where Dr. Davis taught political science for 19 years until retiring in 2002.

Once described as a "brilliant career officer" by former Secretary of State Henry Kissinger, Dr. Davis also served as ambassador to Bulgaria, Guatemala, and Switzerland.

He arrived in Chile in 1971, a year after Allende became Latin America's first democratically elected Marxist president. Dr. Davis' term there ended amid suspicions of American involvement in the 1973 military coup that resulted in Allende's violent death, the circumstances of which are still in such dispute that Chile recently ordered the exhumation of the body.

Dr. Davis discussed U.S. policy toward Allende's government and refuted allegations of American collusion in its downfall in his 1985 book, The Last Two Years of Salvador Allende.

He was the model for the ambassador in the 1982 Costa-Gavras film Missing, which was based on a book of the same name by Thomas Hauser. In 1983, Dr. Davis and two other American officials who served with him in Chile sued Hauser, Costa-Gavras, and Universal Pictures for libel, alleging that false accusations were made of their complicity in the disappearance and death of American journalist Charles Horman during the coup. The suit was ultimately thrown out of court.

Born in Cambridge, Mass., Dr. Davis graduated from Brown University in 1944, the year he received his commission as a Navy ensign. He served on the USS Champlain until 1946.

A year later, he earned a master's degree from the Fletcher School of Law and Diplomacy at Tufts University. He briefly taught at Fletcher, where he earned a doctorate in 1960.

He joined the foreign service in 1947. In 1959, he was an escort officer for Nikita Khrushchev when the Soviet leader toured the United States.

From 1962 to 1965, Dr. Davis was a special assistant to Peace Corps director Sargent Shriver and later was a deputy director. He left the agency to take the post of U.S. minister to Bulgaria.

He was on the senior staff of the National Security Council in August 1968 when terrorists killed John Gordon Mein, U.S. ambassador to Guatemala. Dr. Davis was chosen to succeed Mein and served as ambassador during a violent period in that Central American republic before moving on to another delicate assignment, in Chile.

He was named assistant secretary of state for African affairs under Kissinger in 1975 but resigned after four months because of differences with Kissinger and President Gerald Ford over covert military operations in Angola.

From 1977 to 1983, he taught at the U.S. Naval War College in Newport, R.I.

In a 1986 op-ed piece in the Los Angeles Times, Dr. Davis expressed regret that he, "the old fud of an ambassador," had presented "too many shades of gray" in teaching foreign policy to one student in particular: Oliver North, the U.S. Marine Corps officer who later made headlines for his role in the Iran-Contra affair.

- Los Angeles Times