The National Museum of African American History and Culture, which is under contstruction on the National Mall, will be supported by the Smithsonian Institution’s lates fundraising campaign. (Chip Somodevilla/Getty Images)

The Smithsonian Institution has raised $1 billion in an ambitious $1.5 billion fundraising campaign aimed at collectively strengthening its member institutions, officials said Monday.

The national campaign is a first for the institution founded in 1846, Smithsonian Secretary Wayne Clough said at a Board of Regents meeting, where the campaign was made public.

“It’s the largest, most ambitious campaign for a cultural organization in the world,” Clough said. “We are proud to work to keep the museums free for all Americans.”

The campaign has been in a “quiet phase” since 2011. In the interim, it has received gifts from more than 60,000 donors from every state.

The campaign has several priorities. It will support the building of the National Museum of African American History and Culture, which has received $162 million of its $250 million goal, and renovations at the Renwick Gallery, the National Air and Space Museum and the National Museum of American History. A portion will be dedicated to educational initiatives, and funds are targeted for technological innovations that will digitize collections.

“Digitization is democratization because it allows all Americans to have access,” Clough said.

Many large gifts, including multimillion-dollar donations from the Bill and Melinda Gates Foundation, Oprah Winfrey, David Koch and Boeing, have previously been announced.

Smithsonian officials decided to go public about halfway through the six-year effort, believing they have built enough momentum to raise the final $500 million by 2017.

The collective approach appears to have been successful. In 2009, Clough said the institution raised about $120 million. In the years since the campaign was launched, average annual totals have jumped to $220 million.

“We have done well. We have momentum but we have great ambition,” said campaign co-chair Alan Spoon, general partner of Polaris Venture Partners and a former regent. “We want to have involvement from all corners of the country and the world.”

They have received 192 gifts of $1 million or more, along with $372 million in donations from members of various Smithsonian boards.

Spoon noted that private investment is increasingly important because government support, while generous, is not keeping pace with increased costs. The 2014 federal appropriation was $805 million, or about 60 percent of its budget.

“It used to be north of ­70­­ per­cent,” Spoon said. “We have to actively seek support to supplement the comforting support from Congress.”

Regents David Rubenstein, a co-founder of the Carlyle Group, and Barbara Barrett, an entrepreneur and former U.S. ambassador, are the other co-chairs. Rubenstein has given almost $10 million in various gifts already. “And I’m not done,” he said.

“We are the nation’s cultural institution. It’s a patriotic type of gift,” he said.

The comprehensive effort is similar to large university campaigns that combine various elements, said Gene Tempel, founding dean and professor of philanthropic studies at the Lilly Family School of Philanthropy at Indiana University.

“You get attention out of the big effort,” he said, adding that some of the Smithsonian’s ­A-list donors also bring credibility. “I think it’s a good plan, especially since they are announcing they are two-thirds of the way to the goal. It means they have some traction.”