Leslie H. Gelb, who observed and influenced U.S. foreign policy for decades, as a government official, journalist and president of the Council on Foreign Relations, where he sought to bring common sense to international power struggles, died Aug. 31 at a hospital in New York City. He was 82.

The cause of death was renal failure brought on by diabetes, said his daughter Caroline Gelb.

Dr. Gelb, who was mentored by Henry Kissinger at Harvard, had a wide-ranging expertise in global policy, beginning with an early assignment in the 1960s at the Defense Department, where he edited the Pentagon Papers, a history of U.S. involvement in Vietnam that was later leaked to the press.

He was given the assignment by Defense Secretary Robert S. McNamara in 1967, when the Vietnam War was at its height. Dr. Gelb was given a staff of six and three months to complete the job.

It took 36 people 18 months to complete the project, which resulted in a series of monographs and documents totaling 47 volumes. By the time it was finished in 1969, McNamara was no longer defense secretary. Dr. Gelb was waved away when he brought the finished volumes to McNamara.

The Pentagon Papers detailed — often in forthright terms — a haphazard history, fraught with chaos and ineptitude, of U.S. military and diplomatic efforts in Vietnam.

“Part of the tragedy of Vietnam,” Dr. Gelb wrote in his summary of the report, “was that the compromises our Presidents were prepared to offer could never lead to an end to the war.”

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Moreover, he wrote, before troops were sent to Vietnam, “no systematic or serious examination of Vietnam’s importance to the United States was ever undertaken within the government.”

When parts of the Pentagon Papers were leaked to newspapers in 1971 by Daniel Ellsberg, one of the contributors hired by Dr. Gelb, opposition to the Vietnam War intensified.

Later in his career, Dr. Gelb worked at think tanks, the New York Times and the State Department, where he was a chief negotiator in arms reduction talks with the Soviet Union in the late 1970s. At the Times, he shared a Pulitzer Prize in 1986 for a series of articles about the implications of the Strategic Defense Initiative — dubbed “Star Wars” — proposed during the administration of President Ronald Reagan.

“Publicly, American allies are supporting research,” Dr. Gelb wrote. “Privately, they continue to express the deepest fears that the program will bring a space arms race that will reduce or eliminate the links between American security and their own.”

He later became a foreign affairs columnist and the editor of the Times’s op-ed page. He left the paper in 1993 to become president of the Council on Foreign Relations, a high-powered think tank that has offered advice to presidents, military leaders and diplomats since the 1920s. Its influence has been so powerful, yet undefined, that it is often cited by conspiracy theorists as part of a cabal to institute some sort of global government.

As president of the council, which publishes the journal Foreign Affairs, Dr. Gelb sought to address the growing threat of violence from loosely organized terrorist groups.

“These conflicts have become the scourge of the post-Cold War world,” he told CNN in 2001. “Without empires to suppress these traditional hatreds, the haters in Africa or the Balkans or elsewhere began once again to kill their neighbors.”

After the terrorist attacks of Sept. 11, 2001, Dr. Gelb hoped to gain influence with the White House of George W. Bush.

“Patriotism for a think tank,” he told The Washington Post that year, “is asking hard questions that are unlikely to be asked by political leaders or by journalists. That’s our job. And for us, it’s the highest form of patriotism.”

Then-Vice President Richard B. Cheney was on the Council on Foreign Relations’ board of directors, but the Bush administration moved in a hawkish direction, with the invasion of Iraq in 2003 — “one of the most radical breaks in foreign policy in our history,” Dr. Gelb said.

When some Bush officials predicted a quick end to hostilities in Iraq and Afghanistan, followed by a move toward democratic institutions in those countries, Dr. Gelb was skeptical.

“Elections and people on the street do not democracy make,” he told the American Prospect in 2005. “Democracy really is a series of institutions and attitudes; it’s free press, protection of minority rights, division of power. It’s the confidence that if you lose in elections, you’re not going to lose your basic interests and values or your life. It’s the rule of law. And those things take a long, long time to develop.”

Leslie Howard Gelb was born March 4, 1937 in New Rochelle, N.Y. His parents, Jewish immigrants from Eastern Europe, ran a corner grocery store.

He graduated in 1959 from Tufts University in Medford, Mass., working his way through college as a parking attendant and dishwasher. He joked that he studied political science and international relations because “being a politics major, a government major, was easier than doing anything else.”

At Harvard, where he studied with Kissinger, he received a master’s degree in 1961 and doctorate in 1964, both in government.

He taught at Wesleyan University in Connecticut for a year and worked for Sen. Jacob K. Javits (R-N.Y.) before moving to the Defense Department, where he was director of the policy planning staff.

In the 1970s, Dr. Gelb worked at the Brookings Institution, taught at Georgetown University and was a diplomatic correspondent for the Times. He served in the State Department during the administration of President Jimmy Carter, helping negotiate a strategic arms limitation treaty with the Soviet Union.

Dr. Gelb worked at the Times from 1981 to 1993 and published several books on foreign policy. In his 2009 book, “Power Rules: How Common Sense Can Rescue American Foreign Policy,” he called for a pragmatic approach to international relations but warned that the United States was “at the point of declining as a nation and a world power.”

To retain its influence abroad, he wrote, the United States would first have to improve its infrastructure, health care and education at home.

Dr. Gelb retired from the Council on Foreign Relations in 2003 but maintained a connection with the organization for many years.

Survivors include his wife of 60 years, the former Judith Cohen of New York; three children, Adam Gelb of Atlanta, Caroline Gelb of Brooklyn and Alison Gelb Andrus of Hastings-on-Hudson, N.Y.; and five grandsons.

Dr. Gelb had a knack for summarizing complex ideas in a few pithy words, making foreign policy digestible at the dinner table.

“Fail alone, succeed together,” he said in a 2009 interview with the Institute of International Studies at the University of California at Berkeley. “That’s the moral of this power story, and that’s what we have to understand.”

He added: “What are public intellectuals supposed to do? We’re not supposed to be cheerleaders. We’re supposed to be prodding those with power to think through what they’re doing that will affect us all.”