A water stain mars a historic hang glider at the National Air and Space Museum, part of the Smithsonian Institution. Officials say years of inadequate financing and maintenance have led to widespread disrepair.

WASHINGTON, Aug. 24 - It may not be obvious to the throngs of tourists who flock daily to its famed museums, but the Smithsonian Institution is falling apart.

Ominous drips from strained expansion joints have sprinkled down amid Asian artifacts in the institution's Arthur M. Sackler Gallery. The historic Arts and Industries Building is closed to visitors to protect them from metal panels dropping from its beautiful but dilapidated ceiling. At the National Air and Space Museum, a water stain mars the Lilienthal hang glider that inspired the Wright Brothers to fly. Even the 1940's prototypes of what was to become seemingly indestructible Tupperware were irreparably damaged in a plumbing breakdown.

The world's largest museum complex, the Smithsonian includes 18 museums and galleries, 10 science centers and a zoological park. It is charged with conserving and displaying the country's treasures, both grand and whimsical - the Star-Spangled Banner that flew over Fort McHenry, bits of moon rock from the earliest space missions, the "puffy shirt" worn by Jerry Seinfeld in his hit television series.

But years of inadequate financing and maintenance have led to widespread disrepair that is imperiling the collections, institution officials say.

This month, Congress slightly increased appropriations for the federally supported institution to $621.3 million for fiscal year 2006, up from $615.2 million this year.

But Smithsonian officials say that is not enough to address what a recent audit by the Government Accountability Office determined was a "broad decline in the Smithsonian's aging facilities and systems that pose a serious long-term threat" to its countless artifacts.

Smithsonian officials estimate that it will take a total of $2.3 billion over the next nine years to solve the most pressing problems. The Board of Regents, the institution's governing body, has considered charging entrance fees to compensate for the budget shortfall. Since it was established in 1846, the Smithsonian has never charged for admission, and Sheila P. Burke, the institution's deputy secretary and chief operating officer, said that so far the recommendation had been voted down.

"These are the nation's treasures," she said. "Ultimately we feel protecting them is a federal responsibility."

Private donations have increased over the last decade, officials said. But donors tend to direct money toward exhibitions and programs or, in the case of major contributors, special projects that can be named for them. In September 2000, Kenneth E. Behring, a California developer and philanthropist, gave $80 million to the National Museum of American History, which now has "Behring Center" attached to its name. But the money was primarily earmarked for the design of major new exhibition areas, including a hall devoted to military history that opened last year. "It is difficult to raise money for plaster and plumbing," Ms. Burke said.

"Everyone is holding their breath," said Mark Goldstein, director of the yearlong audit, whose results were published in April. "They have been relatively lucky so far, but who is to say they will be so lucky in the future if they are unable to fix the damage they are currently presented with?"

The vast Smithsonian complex contains more than 136 million objects and specimens. The institution owns and leases buildings in New York, Massachusetts, Arizona, Florida and Panama, but for now, officials said, maintenance concerns are confined to its centerpiece attractions in Washington.

While not always immediately apparent, many of the problems are in plain view. An eight-foot-deep trench splits the gardens covering the underground Arthur M. Sackler Gallery, where an engineering and construction team is working to stop expansion joints from leaking. At the National Zoo, a hundred-year-old sloth bear enclosure and the flight cage for birds of prey were demolished last year because they posed a danger to animals and visitors.

The Arts and Industries Building, completed in 1881 and listed as a national historic landmark, was closed to visitors in January 2004 because of falling metal panels. A day care center and children's theater were hastily relocated following the closing, but several other administrative departments, including the institution's archives and central computer system, are still housed there while new office space is secured. Scaffolding covers doorways to protect staff members from falling bits of plaster and metal.

"It requires a behavior of constant vigilance," said Tammy Peters, acting director of the archives division. "When it rains, we walk around nervously with the wet vac."