James David Barber, 74, who died of a neurological disease Sept. 12 at his home in Durham, N.C., was a Duke University political scientist and provocateur best known for exploring the psychology of Oval Office aspirants and occupants. Many of his classifications for office-seekers, including "active-positive" and "passive-negative," are still used in political discourse.

Dr. Barber could be a devilish and devastating writer and speaker. President Warren G. Harding, he once wrote, was a "wonder of flatulent fellowship."

His sound bites made him a favorite source for journalists. He spent years as a consultant to "NBC Nightly News" and as a board member of the Poynter Institute, a center for the study of journalism and media ethics in St. Petersburg, Fla.

With his best-known book, "The Presidential Character: Predicting Performance in the White House" (1972), Dr. Barber promoted the largely novel idea that voters could discern just as easily as trained psychiatrists how early patterns of behavior could affect a politician once in the White House.

He identified four central categories of presidential types: "active-positive" (high self-esteem, flexible, goal-oriented), "active-negative" (compulsive, power-seeking), "passive-positive" (genial and agreeable but easily wounded) and "passive-negative" (dutiful, withdrawing from political fights).

While reviewers initially called the book refreshing and insightful, others have come to see his classifications as perhaps too arbitrary.

But to Dr. Barber, greatly influenced by Harold D. Lasswell's groundbreaking book "Psychopathology and Politics" (1930), political science was a science. He felt it possible to quantify how political contenders act and react based on their upbringings.

This was a way, he said, to cut through the frozen smiles and relentlessly sunny messages designed to woo voters on the campaign trail.

After Jimmy Carter became president, he wrote: "Shakespeare taught us that one can smile and smile and be a villain; Eisenhower taught us that a smile can conceal a sense of botheration. Even Nixon could smile while his insides ground, and old Bill Taft, with his 'Smile, Smile, Smile' motto, had a largely dismal time trying to be President.

"So it is not to the now-famous Carter grin we must look for signs of political happiness, but to the self, discernible, however dimly and indirectly, in his life experience and his reactions to that experience."

Dr. Barber, the son of a physician and a nurse, was born July 31, 1930, in Charleston, W.Va.

He served in the Army's Counter-Intelligence Corps in the mid-1950s and often recounted the time he held the training rifle so oddly that the bullet shells flew down his shirt and burned his chest.

He felt more comfortable in academia. His interest in politics began as an undergraduate at the University of Chicago, which emphasized the history of ideas through its Great Books program. He later received a master's degree in political science from Chicago and a doctorate in political science from Yale University, where he became a professor and wrote several highly nuanced quantitative analyses of politics.

Dr. Barber was concerned with major social movements of the day. He attended the 1963 civil rights March on Washington and later was director of the Harvard-Yale-Columbia Intensive Summer Studies Program, which brought students from predominantly black southern colleges to study at those Ivy League schools.

Fred I. Greenstein, a fellow Yale doctorate student and now an emeritus professor of politics at Princeton University, said Dr. Barber became increasingly consumed by the course of the Vietnam War. That led Dr. Barber to become "more and more interested in having an impact on public affairs."

He aimed "The Presidential Character" at a general readership, hoping to provide psychological markers for voters to avoid choosing ill-suited presidents, in which he lumped Lyndon B. Johnson and Richard M. Nixon. The book went through four editions, and he updated it to include President Ronald Reagan.

At Duke, which he joined in 1972 as chairman of its political science department, Dr. Barber helped lead the fight against a proposed Nixon presidential library on campus. The idea had been initiated by the university president, Terry Sanford, who became a Democratic senator from North Carolina.

Dr. Barber's last work, "The Book of Democracy" (1995), about building democracies in Third World countries, was nearly impossible for him to finish. His struggle with primary progressive aphasia, which affected his thought and speech abilities, made it hard for him to write and edit.

He retired from Duke in 1995 and became more active in his Episcopal church, where he met Liberian refugees whose plight touched him. He helped establish a system to send school supplies to Ivory Coast, where many of those fleeing war-torn Liberia had settled.

In the mid-1980s, he was chairman of Amnesty International U.S.A.

His marriage to Ann Sale Barber ended in divorce.

Survivors include his wife, Amanda MacKay Smith, whom he married in 1972, of Durham; two daughters from his first marriage, Sara Connor of Boylston, Mass., and Jane Barber Thery of Washington; two sons from his second marriage, Luke Barber of Cherry Hill, N.J., and Silas Barber of Durham; a brother; and two grandchildren.

Political scientist James D. Barber tried to categorize the personalities of presidents and candidates.