Grand and ornate, the nine-foot-tall, decorative marble urns for decades flanked the stage of Arlington National Cemetery's Memorial Amphitheater, adjacent to the Tomb of the Unknowns.

Next weekend, however, the two urns, designed by the same firm that built the New York Public Library and the Russell Senate and Cannon House office buildings, will stand not at the forefront of one of the nation's most venerated shrines but rather are set to be up for sale at the Potomack Company, an Alexandria auction house.

The urns are literally "a piece of history," as the antiques dealer who now owns them likes to say. But their historic value - evident in photos of presidential visits since Woodrow Wilson dedicated the memorial in 1920 - is exactly why preservationists were stunned to learn that they are being sold to the highest bidder.

"It's alarming to see portions of our national legacy being sold off," said Robert Nieweg, director of the National Trust for Historic Preservation's southern field office. "It raises some red flags for us, and we have some very significant concerns about the cemetery's stewardship of this extraordinarily historic place."

How the urns, witness to so many public ceremonies, landed in private hands is something of a mystery. Under the strict procedures the federal government has adopted to protect its property - and particularly artifacts with historic and artistic value - the urns should have been restored or put in a museum, not put out on the open market, preservationists say.

Since 1997, the urns have been at DHS Designs, an antiques shop in Queenstown on Maryland's Eastern Shore. Darryl Savage, the owner, is closing his store and auctioning off his inventory, which includes 14 marble balusters that were part of the railing that rings the amphitheater.

In an interview, he said he acquired the urns from another dealer, whom he would not identify. That dealer, Savage said, acquired them from a company that renovated the amphitheater in the mid-1990s. Savage said the company replaced the urns with modern replicas and was allowed to take away the originals.

The Department of the Army, whose stewardship of the cemetery has been questioned since an investigation found widespread burial problems there last year, confirmed that the contractor, Omni Construction - which later merged with Clark Construction, a venerable Bethesda firm - was to "dispose" of the urns.

But the Army, which learned of the sale of the urns from The Washington Post, has not been able to find the contract and could not provide details about how the urns or balusters were to be disposed of, said Gary Tallman, an Army spokesman.

Missing paperwork has been an ongoing source of trouble as the Army has struggled with management issues at the cemetery. Last summer, Army officials told a Senate committee that they could not find more than a dozen contracts that were part of the cemetery's failed effort to digitize its burial records.

Tallman also could not say Friday whether the cemetery had sought input from the agencies that monitor disposal of government property and preservation of historic artifacts.

"This is just another example of the poor contract management at Arlington Cemetery in recent years, and this cannot continue," Sen. Claire McCaskill (D-Mo.) said in a statement released Saturday. "Both the Army and the contractors responsible for this have some explaining to do to the American people. The Subcommittee on Contracting Oversight will investigate how this happened."

McCaskill is the chairman of the subcommittee, and late last year she co-sponsored legislation to hold the Army accountable for the cemetery's graves.

Eric Fulton, a spokesman for Clark, said a subcontractor on the amphitheater renovation, Pagliaro Brothers Stone of Upper Marlboro, was tasked with disposing of the urns. Bob Benedetti, a Pagliaro vice president, said late Friday that he did not know what had happened to the urns.

"I would suspect that they were back there for crushing," he said. "I'm not sure if someone bought them from someone in the crusher plant or not. I don't recall."

The fact the the urns are now for sale "doesn't bother me," he said. "There is nothing I can do about it. Old stone to us is generally a cost."

The Army, meanwhile, is continuing to investigate how the urns ended up in private hands, and on Friday it asked the auction house to "halt the sale pending additional research to determine rightful ownership and disposition."

Given the unique nature of the urns, Nieweg, of the National Trust, also called on the auction house to cancel the sale and return the artifacts to the cemetery.

Elizabeth Wainstein, owner of the Potomack Company, said she contacted the Pentagon as soon as she got the consignment and was assured that the urns had been removed from the amphitheater in accordance with the renovation contract. She said that Savage, the current owner, has "clear title to the urns and balusters" and "the full right to sell them at auction."

In 2007, a similar controversy erupted after the Army announced plans to replace the monument at the Tomb of the Unknowns because of cracks that zigzagged across its surface. The cemetery argued that the cemetery, known for its rows of meticulously maintained ivory white headstones, had to maintain its pristine appearance.

But preservationists argued that the original monument could and should be repaired to maintain the authenticity of the tomb. Ultimately they prevailed, and the cracks were fixed.

Still, concerns lingered about the cemetery's ability to manage the delicate balance between maintaining an immaculate shrine to the fallen and preserving its historic legacy.

"It was our experience with the cemetery that they were bound and determined to toss the tomb into the garbage and replace it with a mere replica," Nieweg said. "My fear is that if the urns were tossed out in the 1990s, then that's the very kind of policy the Army implemented there: Throw away the authentic elements of this designed memorial and replace them."

Since then, the National Trust has urged the Department of the Army to list the cemetery as a National Landmark on the National Register of Historic Places - a designation that would document the site's monuments and help protect its artifacts.

The cemetery's previous leadership, which was ousted last summer in the wake of the burial scandal, resisted, Nieweg said. In a letter to the National Trust, Kathryn Condon, the new director of the Army cemeteries program, wrote that she was "surprised" the cemetery had not been landmarked and that her staff would look into seeking nomination.

Carol Shull, chief of Heritage Education Services for the National Park Service, which oversees the National Register, said she had assumed the cemetery had been listed. When told it was not, she was incredulous. Shull checked the records, and confirmed that the cemetery is not on the register, but Arlington House, the home of Confederate Gen. Robert E. Lee that sits in the cemetery but is managed by the National Park Service, is.

There is no doubt the amphitheater would be eligible. Located on a bluff overlooking the capital, it's where dignitaries, often including the president, gather for Memorial and Veterans Day ceremonies. It's where President Warren G. Harding, standing between the urns, presided over the interment of remains at the Tomb of the Unknowns in 1921. And it's where Vice President Biden stood last Veterans Day.

Designed by Carrere and Hastings, one of the most prominent architecture firms of the early 20th century, the amphitheater is made of Danby marble quarried from Vermont. Around the frieze above the colonnade are the names of 44 battles from the American Revolution to the Spanish-American War. Above the stage reads a portion of Abraham Lincoln's Gettysburg Address: "We here highly resolve that these dead shall not have died in vain."

After construction was completed in 1920, Washington state's Pullman Herald proclaimed the amphitheater "the most splendid monument to the heroic dead ever erected by any nation." The urns, carved with rams' heads, snakes and eagles, sat atop pedestals in niches that frame the stage, an integral and symbolic part of the memorial.

"They are absolutely gorgeous," said Mark Alan Hewitt, an architect who co-wrote a book on Carrere and Hastings. "They're just superb and very prominent in the design. So to take them off seems very odd."

After years of exposure to the elements, the urns are weathered, and parts of each pedestal are broken. But art historians argue that imperfections often add value to artifacts: The Venus de Milo isn't cherished less because its arms are missing; the Liberty Bell isn't diminished because it is cracked.

Even if the urns were beyond repair, they are, given their lineage and craftsmanship, "museum-worthy objects" that should be on public display, said Kirk Savage, author of "Monument Wars: Washington D.C., the National Mall and the Transformation of the Memorial Landscape." "These are public objects that are owned by all of us, or should be."

After acquiring the urns, Savage initially priced the pair at $125,000. But they never sold. Now the auction house estimates that they could sell for $20,000 to $40,000.

Wainstein, the auction house owner, said she hopes a philanthropist will buy them and donate them to a museum or return them to the cemetery. But she makes no promises as to what might happen on the open market.

"This a public auction and everyone is welcome," she said. "The highest bidder is the winner."