Roger G. Kennedy, the director of the Smithsonian’s National Museum of American History who transformed the stodgy repository often called “the nation’s attic” into a vibrant display that enshrined pop-culture memorabilia even as it confronted some of the most shameful moments in the country’s past, died Sept. 30 at his home in Rockville. He was 85.

He had melanoma, his wife, Frances Hefren Kennedy, said.

Mr. Kennedy, who served as director of the National Park Service after leaving the history museum in 1992, took an unusual path to the top of a major American museum. A prolific author but never an academic, he had held many jobs — Washington correspondent for NBC in the 1950s, banker, vice president of the University of Minnesota and executive with the Ford Foundation in New York.

In 1979, he arrived at the Museum of History and Technology, as the American history collection was then known, without any experience in museum administration but with a visceral passion for the past. “I’ll teach history to anybody I can get my mitts on,” he once told Newsweek.

When Mr. Kennedy began working for the Smithsonian, S. Dillon Ripley, the institution’s top executive, was concerned with strengthening its mass appeal. Like Ripley, who put the carousel on the Mall, Mr. Kennedy cared most about drawing people into the museum and persuading them to stay a while.

Asked about his legacy at the museum, Mr. Kennedy told The Washington Post in 1992, “I would defer to any 15-year-old passing through this place.”

Mr. Kennedy led what current interim director Marc Pachter called the museum’s “golden age.” The building’s name changed to its current one, a move that reflected Mr. Kennedy’s aspiration to house more than a staid collection of collections. He reorganized the trove of artifacts — ranging from stamps to inaugural gowns and machines — to present a broader narrative of the United States.

Exhibits and acquisitions during his tenure included the chair from which Archie Bunker shot off his bigoted mouth on the television show “All in the Family,” forcing viewers to confront an ugly side of American culture in the 1970s; the set of the “M*A*S*H” television show that helped families talk not only about the war in Korea but also the one in Vietnam; and one of the red cardigans Fred Rogers donned every time he asked millions of American children if they would be his neighbors.

Some critics did not warm to the emphasis on pop-culture items, questioning whether the ruby slippers from “The Wizard of Oz” merited a place in the marble halls of a museum that also grappled with slavery and racism.

Mr. Kennedy defended the popular items, saying his hope was to entice people with the fun stuff. “Once we get ’em in the door,” he told Newsweek in 1989, “there are innumerable other things they’ll catch out of the corner of their eyes.”

In style, Pachter said, Mr. Kennedy used the “principles of drama” to make the museum more engrossing. He hired a theatrical designer from the Metropolitan Opera to dream up a display for the flag that inspired “The Star-Spangled Banner.” Once an hour, lights illuminated the flag while the national anthem’s melody rang out over speakers.

In substance, Mr. Kennedy favored untold history, particularly the narratives of minorities long overlooked by many museums.

Leading up to the Constitution’s bicentennial in 1989, the museum opened the exhibit “A More Perfect Union,” about the internment of Japanese Americans by the U.S. government during World War II.

Mr. Kennedy defended the exhibit against charges that it was an inappropriate way to mark the national milestone. Some people, Mr. Kennedy said, “would prefer to dress up models and have them wander around pretending they are Jefferson and Madison.”

“The Constitution isn’t a costume drama of the past upon which the curtain went down in 1789,” he told The Post before the exhibit opened. “I regard this show as a celebration of the openness of the American system. The reason for doing this kind of show is to make it clear that we don’t always get it right, but we keep on trying.”

In the 1987 exhibit “Field to Factory,” the museum chronicled the northward migration of African Americans during the first half of the 20th century. Visitors entered a life-size train station waiting room through two doors labeled “White” and “Colored.” Writing in The Post, critic Lon Tuck called the show an “exhaustive” display that documented “a vital — and somewhat neglected — portion of American social history.”

After 13 years with the museum, Mr. Kennedy moved to the National Park Service, which he led from 1993 to 1997. He distinguished himself from many previous directors by wearing the NPS flat hat, gray shirt and green trousers in a show of solidarity with the rank and file.

A difficult reorganization process, set into motion by the Clinton administration’s downsizing of government agencies, consumed much of Mr. Kennedy’s energy. The new organization was not widely popular within the NPS, former colleagues said, but they credited Mr. Kennedy with saving many jobs that might have been lost.

His most significant achievement, they said, was helping the Park Service see itself not only as the custodian of the magnificent parks of the West but also as the keeper of hundreds of historic landmarks, some famous and others almost unknown.

Roger George Kennedy was born Aug. 3, 1926, in St. Paul, Minn. For several generations, his family ran the Kennedy Brothers Arms Co., a gun shop and expedition outfitter. As a young man, Mr. Kennedy led canoe trips into the waters along the Canadian border.

After serving in the Navy during World War II, he graduated from Yale University in 1949 and from the University of Minnesota law school in 1952. That year, he lost a congressional race against the incumbent, Minnesota Democrat Eugene McCarthy.

Survivors include his wife of 53 years, Frances Hefren Kennedy of Rockville; a daughter, Ruth Kennedy Sudduth of Stow, Mass; and a brother.

Mr. Kennedy’s books included “Hidden Cities” (1994), which explored early Native American civilizations, and “Burr, Hamilton, and Jefferson” (2000), about the character of the founding fathers. Writing in the New York Times, architecture critic Paul Goldberger described Mr. Kennedy’s 1982 study “American Churches” as an “unusual and impressive book” and called the text “thoughtful and even profound.”

In 1993, Washingtonian magazine asked Mr. Kennedy for his views on the Washington Monument.

“Maybe we should have left it as it was initially designed,” he said, “not Egyptian, but a truncated statement of a nation aspiring to grandeur. Or maybe we should have left it when it was unfinished. That seems to me, symbolically, the best phase.”