James R. Schlesinger, who served as secretary of defense under Presidents Richard Nixon and Gerald Ford before becoming the nation’s first energy chief in Jimmy Carter’s administration, has died. He was 85.

James R. Schlesinger, who served as secretary of defense under Presidents Richard Nixon and Gerald Ford before becoming the nation’s first energy chief in Jimmy Carter’s administration, has died. He was 85.

He died Thursday of cardiac arrest, according to former Defense Department official Francis "Bing" West. Schlesinger had been suffering from pneumonia.

The Harvard University-trained economist took the top job at the Pentagon in 1973 and set out to boost the Defense Department’s declining budget and morale after the Vietnam War. More popular with the military establishment than with Congress, he had little success securing funding increases as lawmakers "kept a tight rein on money for his programs," according to the department’s website.

He shifted the administration’s thinking on nuclear weapons, advocating a flexible response of limited strikes to replace the deterrence policy of mutually assured destruction. Schlesinger also emphasized U.S. conventional forces to outweigh the relative parity in atomic-weapons capabilities of the two superpowers, and he urged NATO members to contribute more to upgrade military equipment.

"James Schlesinger was the ideal hawk to exploit the new weaponry developed under a decade of mutually assured destruction," Michio Kaku and Daniel Axelrod wrote in "To Win a Nuclear War" (1987). "Nixon grudgingly acknowledged the man’s command and grasp of nuclear strategy."

Schlesinger confronted multiple foreign-affairs crises during his 28-month tenure. He oversaw the airlifting of supplies to Israel in the 1973 Yom Kippur War; U.S. policy on the 1974 Turkish invasion of Cyprus; the helicopter evacuation of the last Americans from Saigon as North Vietnamese troops overran the city in 1975; and the rescue of the crew aboard the U.S.-registered Mayaguez freighter captured by Cambodia’s Khmer Rouge, leading to the deaths of 41 U.S. military personnel.

Having previously served under Nixon as chairman of the Atomic Energy Commission and the director of the Central Intelligence Agency, Schlesinger was considered a competent administrator even as he struggled on a personal level with colleagues. He remained in Ford’s Cabinet after Nixon’s resignation in 1974 until his ouster as part of the "Halloween massacre" in November 1975 over disagreements with the president and Secretary of State Henry Kissinger.

"His aloof, frequently arrogant manner put me off," Ford said of Schlesinger in "Kissinger" (1992) by Walter Isaacson. "I could never be sure he was leveling with me."

Schlesinger’s personality also grated with Nixon, who once said to his chief of staff, H.R. Haldeman, "I don’t want that guy in my office ever again," according to Kaku and Axelrod.

He fell from favor for impeding the efforts of Ford and Kissinger to secure a strategic arms-control agreement with the Soviet Union and for his uncompromising dealings with Congress over the Pentagon budget. In a flurry of dismissals by Ford, Schlesinger was replaced by Donald Rumsfeld, who at age 43 was the youngest person to run the Pentagon.

Schlesinger, whose intellect Kissinger once described as "my equal," returned to government in 1977 to head the Energy Department created during the Carter administration. Schlesinger was asked to coordinate several federal agencies under one umbrella during the oil crisis of the 1970s, when Arab nations embargoed the delivery of petroleum to the U.S. and other countries. Carter fired him in 1979 in a Cabinet reorganization.

James Rodney Schlesinger was born on Feb. 15, 1929, in New York to parents Julius and Rhea Schlesinger. He attended Horace Mann School in Manhattan before studying economics at Harvard University, earning a bachelor’s degree in 1950, a master’s in 1952 and a doctorate in 1956.

Schlesinger taught economics at the University of Virginia in Charlottesville, Va., for eight years until 1963. During this time, he wrote "The Political Economy of National Security." He then moved to the Rand Corp. and became director of strategic studies there until 1969, when he joined the Nixon administration.

After leaving office, Schlesinger worked for Lehman Brothers, Kuhn Loeb Inc. as a senior adviser and was consulted on defense issues during George W. Bush’s presidency.

Schlesinger and his wife, the former Rachel Line Mellinger, had eight children: Cora, Charles, Ann, William, Emily, Thomas, Clara and James. Rachel Schlesinger, a violinist and board member of the Arlington Symphony in Virginia, died in 1995. A concert hall and arts center is named after her at Northern Virginia Community College.

— With assistance from John Walcott.