Shortly after midnight on March 6, 1854, nine men, said to have been members of the anti-Catholic Know Nothing Party, stole onto the grounds of the Washington Monument, poisoned the watch dog and, at gunpoint, tied up the night watchman.

Using sledge hammers, the men broke up a three-foot slab of marble from a Roman temple, a gift from Pope Pius IX and one of more than 195 memorial stones slated to be placed in the inside walls of the monument honoring George Washington.

The Pope's Stone, as it was called, was carried to the river, then less than 100 yards from the monument, taken in a rowboat to near the Long Bridge (site of the present 14th Street Bridge) and dumped overboard, according to an 1883 Washington Post interview with one of the surviving conspirators.He requested anonymity and was identified only as a Washington "saloon keeper."

No one was ever prosecuted for the crime, despite a $500 reward. And no trace of the Pope's Stone was ever found, although the saloon keeper said several of the conspirators kept pieces of it.

For the past two years, however, an 18-inch marble obelisk, purported to have been carved from the Pope's Stone, has been on display at the Smithsonian Institute.

It was donated by an 86-year-old Oxon Hill woman, Kathryn Wells, who had hidden it in closets for 60 years and had asked that the Smithsonian give it no publicity when she donated it in 1972.

Wells got the stone from former Confederate Army Capt. Joseph A. Ridgway, the brother of one of the conspirators. Wells said she had been afraid to publicly name Ridgway, who had run a saloon in Upper Marlboro, because "some of that family still live hereabouts."

The National Park Service, custodian of the Washington Monument and other Mall memorials, only learned two months ago that part of the stone might still exist. A ranger at the monument was describing the stone's mysterious disappearance to tourists, when one of them said: "Oh, I just saw part of that cover at the Smithsonian."

"That was the first we heard of it," said George Berklacy, local Park Service spokesman."As I told them over there (at the Smithsonian), as far as we're concerned they're harboring stolen evidence. The case of the Pope's Stone is still open and under investigation as it has been for the past 125 years."

Whether the Smithsonian stone actually is part of the original Pope's Stone remains an open question, Berklacy suggests. Monument records describe the Pope's Stone as "cream colored" marble; a newspaper account of the day called it "black and grey," and the Washington saloon keeper told The Post in 1883 he remembered it as "white-looking marble, striped."

The stone from Ridgway now on display in the We The People exhibit at the Museum of History and Techonology, is a dark red, variegated marble.

The 36- by 18- by 10-inch marble slab sent by the Vatican, from the ruins of the Temple of Concord in Rome, was built of "costly variegated marbles in 366 B.C." according to a history of the Roman Forum. No known trace of the temple remains today with which to compare the Smithsonian marble, unless the Vatican has other relics stored away. The Vatican was never officially informed of the disappearance of the Pope's Stone, according to monument records.

Whether the Smithsonian has part of the original Pope's Stone or not, "they do have five other stones of ours over there," says Berklacy, "since the last record we have of them is an 1888 note from the Smithsonian's assistant secretary saying they were sending over a wagon to the Washington Monument to pick them up for display."

Those stones also have disappeared, "but that's not surprising since they can't even find their own cornerstone over there," said Berklacy, a former public information officer at the Smithsonian.

The location of the cornerstone for the Smithsonian's red sandstone "castle" on the Mall is unknown, although museum officials searched and researched the building thoroughly in 1966.

But the Park Service is hardly the one to cast the first stone since it cannot locate the cornerstone for the Washington Monument, Berklacy concedes.

Both cornerstones have leaden boxes filled with coins, newspapers clippings of the day (1848 for the Washington Monument and 1847 for the Smithsonian building) and other historical memorabilia. The cornerstones are somewhere below the present ground level. They're not lost. They just cannot be found.

But the disappearance of huge marble and granite stones, some weighing more than a ton, plagued the Washington Monument before its cornerstone was even laid when memorial stones began arriving from all over the world.

The Pope's Stone was one of the earliest to arrive and one of several from ancient temples and Old World buildings sent as tributes to America's first president.

The idea of installing memorial stones inside the monument came from an Alabama doctor, who suggested that each state send an inscribed stone.The Washington National Memorial Society, a semi-public group formed in 1833 to build a memorial to Washington, extended an invitation to the world to send tributes in the form of memorial stones - and money, too, since lack of funds was delaying construction of the monument.

The requests produced the odd assortment of almost 200 memorial stones that now adorn the inside walls of the monument for 400 of its 555 feet.

None has been visible for the past seven years because the monument's 897 steps were closed to the public in 1971 following a near-fatal accident, in which a boy climbed the elevator scaffolding. The Park Service reopened the steps Memorial Day weekend, but only for groups to descend the steps accompanied by Park Service rangers.

It was the stones that got away, however, that have caused the most controversy.

Park Service workers Ellen Barrie and Malcolm Wilbur, unearthing information about the stones from the National Archives and records the Park Service had gotten from the monument society, recently discovered the note linking the Smithsonian with five of the missing stones. They also found records of one other missing stone and found the 189 stones installed the monument inside the monument actually numbered 188.

The five the Smithsonian borrowed, and apparently lost, included a 2,000-year-old head or bust from the Temple of Augustus in Egypt, a stone from a 1388 Swiss Chapel honoring William Tell, part of the Temple of Aesculapius from the Greek Island of Paros (sent by some U.S. naval officers) a marble slab from the "Citizens of Alexandria, Va., descendants and neighbors of Washington," and a three-foot granite slab with "G" inscribed on it, the donor of which was unknown to monument record keepers of the 1850s.

Herbert Collins, Smithsonian director of political history who put the alleged Pope's Stone on display during the Bicentennial, does not vouch for its authenticity. However, he said the Smithsonian has done almost everything possible to find the five missing stones the museum apparently borrowed. They were probably stored outdoors, said Collins, "and anything can happen to a pile of stones."

Besides those five stones, at least two others sent for the monument disappeared - one from the Napoleon's Tomb in Paris, a gift from France, and one from the ruins of Carthage (now a suburb of Tunis).

The French stone was last seen in the Brooklyn Navy Yard in 1861 wrapped in French and American flags. The Carthage stone disappeared in the 1850s, but in 1959, when the present elevator in the monument was being installed, Park Service workmen found the stone under stone steps.

But the most sensational disappearance was that of the Pope's Stone.

That title was learned about the disappearance until decades later when former Know Nothinngs confessed anonymously is hardly surprising. The American, or Know Nothing, Party was a secretive organization whose members, when asked about the party, replied "I know nothing."

And the night watchman at the Washington Monument was thought to have a Know Nothing or at least a sympathizer. The guard, who was carrying a shotgun loaded with buckshot, was roped inside his outhouse-like watchman's shack for more than four hours while the Pope's Stone was carried off. He was fired immediately after the incident.

The purported piece of the Pope's Stone at the Smithsonian has had an equally secretive existence. Not only did Wells hide it in her closet for 60 years, she didn't even tell other members of her family about it until a few years ago.

Wells was given the obelisk in 1961, she said, when Ridgway brought it home from his Upper Marlboro saloon, which had just been sold to the Catholic Bishop of Baltimore for use as a church hall. The saloon known as Gibbons Hall, was torn down recently, Wells said.

"We were neighbors in Upper Marlboro and I had tended his blind wife for 20 years, even since I was 4 years old," Wells said. "He was passing by one day - May 6, 1911 -carrying a heavy bundle of papers and I asked if I could help carry it . . . he was a little short fellow and very old. He said no but he had something inside for me, in five parts, for helping his wife. He said she didn't know anything about it and hoped it wouldn't be too much of a shock for her.

"He told me it was a marble monument that had been carved from a piece of the marble sent to America from Rome by Pope Pius IX to be put in the Washington Monument, but was destroyed by a gang of Know Nothings . . . including his brother."

Wells said Ridgway's brother gave him the stone, when the brother's health was failing, and had told Ridgway to keep it hidden until after his death. Wells said she kept it hidden until after Ridgway died . . . "and he lived to be almost 100."

When she gave it to the Smithsonian, accoridng to curator Collins, "At first she didn't want it on exhibit, but she would still call and ask about it, always in a secretive whisper, a very low voice." She finally agreed to let it be displayed, Collins said, although at first she wanted it to have no publicity.

The obelisk at the Smithsonian was carved by a friend of Ridgway's brother, Wells was told. It has not inscription or other markings on it. The Pope's Stone apparently was inscribed, "Rome to America," although records are not clear on the subject.

The Washington saloon keeper who "confessed" to The Post in 1883 said that what he saw in the predawn darkness was a stone "with a Latin inscription in gilt letters on it," although the story later said the block had no inscription but was to have the words "From Rome" carved on it when it was placed in the Washington Monument.

One of the ironies of the destruction of the Pope's Stone, said Wells, is that both she and Ridgway, who between them were custodians of the marble obelisk for 120 years, are Catholic.Ridgway's Know-Nothing brother, she said, was "lapsed. It shows you can't beat the church."