Penn Kemble, 64, a political activist who considered himself a "muscular Democrat" and who kept himself in intellectual fighting trim by engaging in policy tilts with adversaries on both the left and the right, died Oct. 16 of brain cancer at his home in Washington. A former acting director of the U.S. Information Agency, he was in recent years senior scholar at Freedom House, a nonpartisan, pro-democracy think tank.

Mr. Kemble believed in a robust internationalism in the tradition of former senator Henry M. "Scoop" Jackson (D-Wash.). He also had an affinity for organized labor, which was, in his words, "the balance wheel of democracy."

During his career, he helped found or lead a number of advocacy groups, including the Coalition for a Democratic Majority.

A friend and former colleague, Joshua Muravchik, resident scholar at the American Enterprise Institute, noted that Mr. Kemble's political and intellectual journey traversed a path from democratic socialist to social democrat. It was a journey similar in its rightward arc to that of many prominent neoconservatives. Although he occasionally took such positions,Mr. Kemble stopped short of leaving the Democratic Party and never considered himself a neoconservative.

He believed, for example, in building a democratic Iraq but sharply criticized the Bush administration's approach on the country. "The distinction between liberation and democratization, which requires a strategy and instruments, was an idea never understood by the administration," he told the New Republic last year.

Richard Penn Kemble was born in Worcester, Mass., and grew up in Lancaster, Pa., where he was a small but feisty football player in high school. His political activism began at the University of Colorado, where he helped establish the Colorado chapter of the Young People's Socialist League.

After receiving a bachelor's degree in 1962, he moved to New York and took a job as a copy boy at the New York Times. His journalism career ended shortly afterward, when the typesetters went out on strike and he refused to cross the picket line.

He stayed in New York and immersed himself in socialist politics, seeking to resurrect the youth section of the Socialist Party, famously led earlier in the century by Eugene V. Debs and Norman Thomas.

Muravchik, who also was part of the movement, recalled that Mr. Kemble stood out as a "good-looking, neatly dressed WASP" in what was otherwise "a scruffy-looking crowd" made up primarily of young Jewish intellectuals.

He was one of the few whites among the leadership of the East River chapter of the Congress of Racial Equality, once staging a sit-in that blocked the eastbound lanes of the Triborough Bridge during rush hour. The aim was to force commuters to ponder the plight of Harlem residents before arriving back at their comfortable homes in the suburbs.

In 1967, he founded Negotiation Now!, which demanded an end to the bombing of North Vietnam and a negotiated end to the war.

In the early 1970s, Mr. Kemble moved to the District and plunged into Democratic Party politics. After the party's 1972 presidential debacle, he helped found the Coalition for a Democratic Majority. Associated primarily with Sens. Jackson and Hubert H. Humphrey (D-Minn.), the group sought to move the party back toward the center and refocus its reliance on a traditional blue-collar base.

Mr. Kemble served as executive director of the group from 1972 to 1976, when he joined the New York senatorial campaign of Daniel Patrick Moynihan. He was Moynihan's special assistant and speechwriter until 1979.

During the Reagan administration, he founded a group called PRODEMCA, or the Committee for Democracy in Central America. He caused consternation among many fellow Democrats by advocating support for the anti-communist contra rebels in Nicaragua. He sought a democratic middle way between communist Sandinistas and former supporters of rightist dictator Anastasio Somoza.

He worked in the Clinton presidential campaign in 1992 and was appointed deputy director of the USIA in 1993. He became USIA's acting director in 1999. In recent years, Mr. Kemble sought to maintain a network of American social democrats. From his sickbed, he conceived and helped organize a conference dedicated to the thought of philosopher Sydney Hook, an intellectual model for Mr. Kemble of the politically engaged social democrat. The event took place Oct. 1.

His marriage to Charlotte Roe ended in divorce.

Survivors include his wife of 22 years, Marie-Louise "Mal" Caravatti of Washington; two sisters, Sara Kemble of Columbia and Eugenia Kemble of Washington; and a brother, Grover Kemble of Morristown, N.J.

Mr. Kemble was in many ways still a socialist, his wife said. "He believed in the public sector as a civilizing force," she added. "He believed in a role for government."