Washington ? Oscar the Grouch probably won’t be happy about his next home: a cold, dark box that is far from “Sesame Street” and his beloved trash can.

The puppet is among tens of thousands of exhibits and artifacts that will be carefully stored as the Smithsonian Institution’s National Museum of American History prepares for a massive, two-year renovation.

The museum closes today. Many items in the way of the construction will be relocated to the building’s wings, where they will be protected from the dust. They include Oscar, the first ladies’ evening gowns and 4,000 lighting devices dating from the early 17th century.

“It’s similar to moving your china cabinet, but not really,” associate curator Stephen Velasquez said. “We very carefully – emphasize carefully – transfer each object.”

Protecting the museum’s collection has been an enormous undertaking. Most tourists see only a small percentage of the museum’s 3.5 million items, such as the Star-Spangled Banner, the 30-by-42-foot flag that inspired the words for the national anthem.

Many items were already stored at the museum and at facilities in suburban Maryland and Virginia; others are part of exhibits on loan to the Smithsonian’s partners.

Curators and conservators have been planning for the renovation for months. It can take weeks to move a vast collection of silver tea sets, flatware and ordinary Tupperware into temporary storage.

Beth Richwine, objects conservator at the Smithsonian's National Museum of American History, explains how they are preparing C3PO, left, and R2D2 from Star

As for the Star-Spangled Banner, it will be carefully rolled up and placed in a crate. And Oscar the Grouch will get extra padding inside his body to prevent new wrinkles on the aging puppet.

The biggest construction worries for conservationists are humidity and temperature changes, excessive dust and potential vibrations from the construction.

The exact relocation and storage costs aren’t available, but they have been included in the museum’s operating budget and in the $85 million renovation project.

The renovation comes four years after a commission report sharply criticized the museum’s layout and presentation, calling them confusing.

Starting this fall, workers will slice through five floors of the building to create a new skylight and atrium that will be the core of the new exhibition space scheduled to open in 2008. The Star-Spangled Banner will be the centerpiece, with a dramatic new gallery that will use special lighting to depict “the dawn’s early light.”

Designers will also add new exhibit walls and open spaces to make the museum easier to navigate.

The renovation will bring the most significant changes since the museum opened in 1964 as the Museum of History and Technology.

Several exhibits already have closed, including “The American Presidency: A Glorious Burden” gallery and the popular “First Ladies: Political Role and Public Image” exhibit.

Some of the most popular objects are being cleaned and prepared for exhibition elsewhere while the museum is closed. Dorothy’s ruby slippers from “The Wizard of Oz” will be part of the exhibit opening Nov. 17 at the nearby National Air and Space Museum, along with R2D2 and C3PO from “Star Wars,” President Lincoln’s top hat and artifacts from Hurricane Katrina.