David Cohen, 79, the Philadelphia-born former president of the advocacy group Common Cause who for more than four decades campaigned for greater government transparency and accountability as a leader in the corps of activists known as public-interest lobbyists, died Sunday at his son's home in Westport, Conn.

The cause was a heart attack, said his son, Aaron Cohen.

"I have never heard a parent say, 'I want my child to be a lobbyist,' " Mr. Cohen once quipped, reflecting on the dim view commonly held of Washington insiders who use their savvy or clout to push their clients' interests among policymakers.

But Mr. Cohen saw himself and his colleagues not as representatives of special interests but as advocates for what he thought to be the common good.

Mr. Cohen, a Temple University graduate, joined Common Cause in 1971, a year after the nonpartisan organization was founded by John Gardner, a Republican who served as secretary of health, education and welfare in the Johnson administration. Mr. Cohen was president from 1975 to 1981.

A self-described people's lobby, the group began with 4,000 members who paid $15 in annual dues and voted on policy positions. Today it has more than 400,000 members and supporters, according to its website.

With Mr. Cohen's participation or leadership, the group was credited with helping to marshal opposition to the Vietnam War, break down the seniority system in Congress that had consolidated power among entrenched committee chiefs, and enact ethics, conflict-of-interest, and open-government legislation after the Watergate scandal.

He remained a prominent figure in Washington advocacy for years after he left Common Cause.

"He really understood very well how you form coalitions," journalist Elizabeth Drew, a longtime friend, said. "He had kind of X-ray vision of the city."

After college, Mr. Cohen's first job was with an upholsterers' union. He went to Washington in the early 1960s and became legislative representative of Americans for Democratic Action, a left-leaning activist group.

With his wife, Carla, he was a part-owner of Politics & Prose, the independent bookstore in Washington that became a gathering place for literary events.

She died in 2010 after 52 years of marriage. - Washington Post