Director Earl A. “Rusty” Powell III, the Director of the National Gallery of Art. (Jabin Botsford/ The Washington Post)

With the reopening of I.M. Pei’s modern East Building last month, the National Gallery of Art is celebrating its 75th anniversary with a freshness and energy that marks a dazzling rebirth of Washington’s flagship art museum.

“To me, it’s a new National Gallery of Art,” said Director Earl A. “Rusty” Powell III. “It’s a much different collection than when we opened. It’s a milestone moment in the history of the National Gallery.”

Pei’s iconic building, with its dramatic angles and sleek lines, has been updated with subtle additions that emphasize the ­artwork.

“It’s really about the art breathing life into the space,” said architect Perry Y. Chin, a ­longtime associate of Pei’s who created the concept design for the project.

Added Susan Wertheim, the gallery’s chief architect: “We knew about the building’s special potential. It just needed to be uncorked.”

Larry Rivers’s "Maquette for Larry Rivers Exhibition at Dwan Gallery," 1961, is on view at the “Los Angeles to New York: Dwan Gallery 1959-1971” exhibit. (Collection of Virginia Dwan/National Gallery of Art)

The three-year, $69 million renovation allowed museum officials to dramatically reimagine the way they display their modern and contemporary collection, which has grown dramatically since 1978, when the Pei building first opened. More than 500 works of modern art are on view in 362,000 square feet of ­galleries.

“It’s not hubris or arrogance to say what the gallery was founded on is quality, quality of the building and quality of the collection,” Powell said. “We’ve always been true to that. We treat this building as a work of art.”

While the building was shuttered, the museum acquired a striking number of works — many from the Corcoran Gallery of Art. The new installation of the permanent galleries benefits from these additions.

It also benefits from more gallery space and from rooms that are now connected. Although subtle, these improvements allow the museum’s modern art curator, Harry Cooper, to tell a story spanning multiple galleries and more than 100 years. Wall text emphasizes the connections between movements, as new stairways and elevators allow visitors to follow the narrative in a seamless path. The renovation includes a black room for video, another first for the generally conservative NGA.

“These are mini revolutions,” Cooper said. “For the first time to present the collection in chronological order, incorporating works on paper and video. It’s a change of procedure for us.”

The East Building’s new sculpture terrace, features Katharina Fritsch's "Hahn/Cock", background, seen through George Rickey's "Divided Square Oblique II", foreground. (Bill O'Leary/The Washington Post)

A sculpture garden on the terrace is another significant change, as is the prominence of pieces accessioned from the collection of the now-defunct Corcoran. From Sam Gilliam, Andy Warhol, Martin Puryear and Jenny Holzer, these works emphasize the gallery’s history as a “collection of collections,” as Powell described it at a pre-opening event.

Two temporary exhibitions featuring promised works extend this idea. “Photography Reinvented: The Collection of Robert E. Meyerhoff and Rheda Becker” comprises 30 photographs by important artists, a promised gift that will strengthen and deepen the museum’s photography holdings. And “Los Angeles to New York: Dwan Gallery 1959-1971” charts the career of art patron and gallery owner Virginia Dwan. The 100 works in the temporary exhibition are part of a larger pledge of her renowned collection.

Although individually subtle, the changes to the East Building and the permanent collection together create a powerful new experience for visitors.

“It’s been a kind of revelation that the building can do all of this,” Cooper said.