Charmaine Jefferson usually knows when Lonnie G. Bunch III is prospecting in her back yard.

Bunch periodically slips into Southern California in search of money and historical objects for the National Museum of African American History and Culture, the symbolically potent, $500 million project that breaks ground Wednesday on the Mall.

Jefferson, executive director of the California African American Museum, hears about it some way, somehow — then lets Bunch know that she knows.

“I always tease Lonnie: ‘I heard you were coming to California; I’m locking the doors,’ ” Jefferson said. “Or: ‘Uh-oh, I heard you were in town. I thought I felt somebody’s hand in my pocket.’ ”

Behind the good-natured joking, though, there are real anxieties about the impact that the long-dreamed-of National Museum of African American History and Culture might have on smaller institutions that cover some of the same territory.

Even as they’ve celebrated the creation of a massive national museum to tell the once-marginalized story of blacks in America, some executives at African American museums have voiced concerns about competing with a Smithsonian museum for money, artifacts and attention.

“I couldn’t be more thrilled that we will have a museum on the Mall dedicated to this history and culture,” Jefferson said from Los Angeles. “It’s extraordinary.

“At the same time, there’s apprehension and fear amongst many that people won’t support all the other black museums that have existed for so long . . . that everybody will be distracted by the new, bright, shiny museum that’s got all the hype. That is not an outcome that anybody wants.”

The National Museum of African American History and Culture isn’t scheduled to open until late 2015, but the excitement surrounding the final Smithsonian outpost on the Mall is building.

Bunch, the museum’s founding director, and his staff have raised about $100 million in private funds and collected roughly 20,000 artifacts for the 374,000-square-foot museum, which has been nearly a century in the making.

It will sit on a five-acre site next to the Washington Monument, in the symbolic heart of American history, a place where blacks have long felt underrepresented. When it opens, the museum is expected to draw between 3 million and 3.5 million visitors each year, Bunch said — attendance that would vault it ahead of all but three of the other Smithsonian museums.

As a federally commissioned institution that will be the largest anywhere to focus on African Americans, it was inevitable that it would cast a long shadow across the U.S. community of black historic sites and museums. There were more than 300 of them in 2008, when the Association of African American Museums last counted, from the 800-square-foot African American Museum of the Arts in DeLand, Fla., to the 125,000-square-foot Charles H. Wright Museum of African American History in Detroit.

Bunch, who is sensitive to his peers’ concern, said he began thinking almost immediately about what it would take for the other museums not just to survive but to soar in the Smithsonian’s considerable wake. Two weeks after starting his job in 2005, he made a promise in a speech to the museum association: He would help the other museums, not hurt them.

“A lot of African American museums were scared,” Bunch recalled. “But through the totality of what we do — the programs, the excitement we create in communities, pushing people in a very concrete way back to local African American museums — I think we’ll ultimately make sure that all boats rise.”

In fact, other museums have benefited from some of the initiatives launched under Bunch’s direction, according to association President Samuel W. Black, who praises Bunch for “not forsaking the African American museum community.”

Those initiatives include a touring artifact-preservation program, a series of traveling exhibitions booked into museums large and small, and an office of partnership and collaboration to advise and assist other institutions.

Bunch also has been talking up plans for an interactive resource center that would show the Smithsonian’s visitors what African American history and culture they could be exploring at institutions back home. And at fundraising events across the country, Bunch has introduced local, regional and state museums to potential donors.

“He is furthering the work we do as a collective,” Black said, “and bringing a greater profile to all African American museums.”

‘A place of pilgrimage’

The push for a focal point for African American history in Washington began in 1915, when black Civil War veterans asked for a monument on the Mall. They did not get one.

In 1929, Congress passed legislation to build an African American memorial. But the project wasn’t funded.

In the 1980s and 1990s, Congress debated the creation of a permanent African American Smithsonian museum, but the idea was squashed by Sen. Jesse Helms, the North Carolina Republican, among others.

Then, in 2003, not long after Helms left office, President George W. Bush signed the museum’s authorizing legislation.

The mandate: Tell the complete story of the black experience in America — “a story all Americans were shaped by and need to know,” Bunch said. When the Smithsonian surveyed people about their expectations, 60 percent of white respondents said they thought the new museum would be for them, too.

But Smithsonian officials acknowledged the obvious: It will be especially significant to African Americans. “This place will also be a place of pilgrimage,” predicted Smithsonian Secretary G. Wayne Clough, likening it to the Martin Luther King Jr. Memorial, which opened last year. The new monument “is sacred,” Clough said. “I think this museum will be as well.”

At Elizabeth Baptist Church in Atlanta one recent Sunday, Rep. John Lewis (D-Ga.), who began pushing for a national black museum when he arrived in Congress 25 years ago, shared the news that construction was about to begin. “They stood and cheered,” Lewis said. “The rank and file of African Americans get it.”

At Wednesday’s ceremony on the Mall, just blocks from the former site of slave pens, Lewis will stand with President Obama, who is scheduled to speak.

Then construction will commence on an institution whose scope, Bunch said, will help set it apart from existing African American museums, where you might learn about slavery or blues music or painter Jacob Lawrence or segregation or the civil rights movement or baseball’s Negro leagues. “But you can’t go many places and learn about the sweep,” he said.

The prospect is thrilling, said Beverly Robertson, president of the National Civil Rights Museum in Memphis. But it is also fueling her sense of urgency to complete a $40 million fundraising campaign for her museum at the Lorraine Motel, where King was assassinated in 1968. She’s more than halfway there, she said.

“We have to get the rest out of the way — another $19 million — before the museum on the Mall is full-throttle focusing on fundraising,” Robertson said. “I want to be done when their development arm is ambitiously moving forward. There’s only so much money.”

Or is there?

Bunch needs to raise $250 million in private contributions to get the new Smithsonian museum built. He’s at $100 million.

“It just goes to show you that while we’ve been underway and have raised an awful lot of money, there’s still money supporting other museums,” he said. “I’m not always going to be able to make sure everybody benefits at every moment. I’m not naive enough to not know that there will be collections that come my way or money that comes my way. There’s always going to be concerns. But I want us all to benefit.”