The Smithsonian's National Museum of American History is planning an overhaul that could involve closing all or part of the museum for extended periods.

Renovations range from creating a new gallery for the museum's iconic Star-Spangled Banner, which inspired the national anthem and is now too fragile to hang vertically, to more mundane work such as repairing the 41-year-old museum's mechanical, electrical and plumbing systems. Infrastructure renovations alone could cost up to $50 million.

Additionally, museum Director Brent Glass said yesterday, he is hoping to "create an architecturally attractive museum -- a museum for the 21st century." Part of that includes trying, he said, "to bring in more light, make circulation easier for visitors, put more of our collection out on view."

The 200,000-square-foot museum, which owns Edison's light bulb, Ford's Model T, Archie Bunker's chair, Julia Child's kitchen and Dorothy's ruby slippers from "The Wizard of Oz," is one of the Smithsonian's most popular attractions, drawing almost 3 million visitors a year. Glass was reluctant to discuss "when we would start and whether we would actually close the museum."

Glass is considering whether the renovations to the museum can be done one floor at a time, or one half of the museum at a time. But closing is also an option, he said -- "one option that was presented to us by the architect as a way of accomplishing our objectives."

Martha Morris, a former deputy director of the museum and an associate professor in museum studies at George Washington University, says "there is a lot of discussion about closing the building." She wrote an article for Museum News about museum construction projects last year.

"It probably would be less expensive to do it when the building is closed," she said yesterday. "If you stay open during renovations, it could cost the museum more money, but I don't really know . . . their final decision."

A year and a half ago, on the museum's 40th birthday in January 2004, officials announced plans to do some of these renovations; they had hoped to be 65 percent of the way through the planning and design process by this summer.

Instead, Glass said, the museum is 35 percent of the way through that process.

"We're revising some of the scope of the work," he said, adding, "We really don't have a timeline. We want to do this the right way."

The museum's age shows not only in that much of the building is not up to code, but also in its dark, boxlike interior, where visitors can easily get turned around and confused.

Its entrance on Constitution Avenue brings museum-goers into the first floor, while the entrance off the Mall ushers people into the second floor -- and sometimes people "end up on the other floor, by the other exit," asking, "Wait a minute. Where'd my exit go?" says museum spokeswoman Valeska Hilbig.

Glass has high expectations. He says he's intrigued by what the Museum of Modern Art in Manhattan accomplished with its renovations (which required closing MoMA and moving its exhibits, in the meantime, to a satellite location in Queens). He's interested in the Smithsonian's newest addition to the Mall, the Museum of the American Indian, which "has done some interesting work on collection displays -- how they locate their display cases, how they provide access, the use of digital technology on the exhibit floor itself," he said. "We always need to learn from other museums."

Still, closing completely is a dicey option, especially given the situation with the Smithsonian's American Art Museum and National Portrait Gallery. Both are in the historic Patent Office Building at Eighth and G streets NW, next to MCI Center. It was closed in 2000 for a complete remodeling and overhaul of the heating, ventilating and air conditioning.

Originally, the museums were to reopen in 2003. Then the deadline was moved to 2005. Today, they are scheduled to open in July 2006. If all goes as currently scheduled, what started as a three-year closure will wind up being twice that.

Smithsonian officials cringe when the Museum of American History is compared with the Patent Office museums.

"Let's let the years speak for themselves," says Smithsonian spokeswoman Linda St. Thomas. Construction on the Patent Office began in 1836, she says, while the history museum was built in 1964.

Already, the museum has received $13 million in funding from Congress for such work as getting "the box," as the museum is called by some, up to code with its fire detection and alarm systems, public restrooms, elevators, escalators and emergency exits, St. Thomas said. In all, such infrastructure renovations are expected to cost the government $45 million to $50 million, while the still-to-be-determined cost related to reshaping the galleries will probably come from the private sector, she said. The museum has hired Skidmore, Owings & Merrill for the job.

Glass notes that, though the museum may be devoted to history, it's cloaked in a '50s and '60s design. He would like to make it more current.

American History is the Smithsonian's third most popular museum; only Air and Space and Natural History attract more visitors.

The 41-year-old National Museum of American History's infrastructure and exhibit spaces need renovation.