Pope John Paul II's mass on the Mall next month for upward of a million people will be an unprecedented event in this capital city, symbolic of the influence and importance of the Roman Catholic Church in American life. But it was not always so.

Indeed, less than half a mile from the spot in front of the Smithsonian Castle where the pope will officiate there occurred, a century and a quarter ago, one of the most blatant anti-Catholic acts in the city's history: the theft of "the Pope's Stone," a gift of Pius IX.

The National Intelligencer, the premier Washington newspaper of the time, began its account on March 8, 1854, this way:

"A Deed of Barbarism was enacted on Monday morning last, between one and two o'clock, by several persons (number not known, but supposed to be from four to 10), which will be considered as belonging rather to some of the centuries considerably in our rear than to the better half of the boasted nineteenth. We refer to the forcible seizure from its place of deposits, in a shed at the Washington Monument, of a block of marble sent hither from Rome, as a tribute to the Memory of Washington, by the Pontiff, and intended to become part of the edifice now erecting to signalize his name and glory. It originally stood in the Temple of Concord at Rome, was of beautiful texture and had for its dimensions a length of three feet, height of eighteen inches, and thickness of ten."

The Washington Monument Society, a group of private citizens, had begun the project and the cornerstone had been laid on July 4, 1847. Along with cash contributions the society received donations of numerous memorial stones, 188 of which eventually were set into the interior walls where they remain visible to those who use the stairs. These gifts came, for example, from the states of Connecticut and Vermont, the cities of Philadelphia and New Bedford (depicting a whale), the Cherokee Nation, several temperance organizations, a Methodist Sunday School, and a group of Chinese Americans. One stone, presented by Greece, had been taken from the Parthenon.

Inscriptions ranged from Chinese and Greek to Hawaiian as well as English. By one account the Pope's Stone bore a Latin inscription. Another account said it read, "From Rome to America."

The Intelligencer report of the theft implied that the night watchman, later suspended, was in cahoots with the thieves, for he raised no alarm until long after the stone was dragged to the Potomac banks, then less than half a mile to the west, and "probably" put in a scow to be dumped into the river.

The year 1854, the time of the theft, turned out to mark the high tide of political influence in the United States of a group of anti-Catholic bigots known as Know-Nothings, a term that has come down to us as derisive. A more or less secret society, the Know-Nothings were composed of Protestants objecting to the recent wave of Catholic immigrants.At first calling themselves Native Americans, the members had the habit of replying, "I don't know," to questions about what they stood for. They soon were tagged as Don't Knows and then as Know-Nothings, usually hyphenated.

Rutherford B. Hayes commented in 1854: "How people do hate Catholics, and what happiness it was to thousands to have a chance to show it in what seemed a lawful and patriotic manner." He was writing of Know-Nothing political power as demonstrated in several states in that year's elections. The next year Abraham Lincoln wrote to a friend: "When the Know-Nothings get control, [the Declaration of Independence] will read, 'All men are created equal except Negroes and foreigners and Catholics.'"

A year after the thievery, the Know-Nothings stole the Monument Society records and "elected" their own officers. Before they tired of the project they managed to add two courses (four feet) of stone. At the advent of the Civil War, however, the monument had reached only 154 feet of its eventual 555. Not until 1880 did Congress step in to provide federal funds and the Army Engineers to complete the job. The Know-Nothings' courses first were removed.

In 1883 when the Potomac was being dredged, a local saloon keeper told a Washington Post reporter who gave him anonymity: "If the dredges . . . strike the right spot, they will fish up something that will create a sensation," the Pope's Stone "that we Know-Nothings dropped into the river nearly thirty years ago." It was not found, but the man's story remains the most likely account of what had occurred.

At a Know-Nothing meeting at Thorne's Hall on Seventh Street, there was talk "about the shame of having a stone from any king or potentate inserted in the monument . . . ." Lots were drawn and nine were chosen. By this account, the watchman was put under armed guard while other thieves hauled the stone on skids from the shed to the scow. The stone was described as "about 4 feet by 1 1/2 feet in size, of a peculiar kind of white looking marble, striped and with a Latin inscription in gilt letters . . . ." The culprit recounted that a piece was chipped off one corner "about the size of two bricks" as a souvenir before the stone was "eased . . . over the side of the scow and away it went with a splash to the bottom of the river" near the Long Bridge, about where the 14th Street spans now stand.

The completed monument was dedicated by President Chester Arthur on a wintry Washington's Birthday, 1885. The story would end here except for one odd sequel.

In 1972 an 86-year-old Oxon Hill resident gave the Smithsonian an 18-inch obelisk, composed of five pieces of mottled reddish stone, purported to have been cut from the Pope's Stone. She said it had been given her in 1911 by an Upper Marlboro saloon keeper whose brother had been one of the conspirators. Today the inscriptionless obelisk can be seen in the Museum of History and Technology, displayed among various gifts to this nation from foreign leaders. A label probably goes too far in assuming its authenticity.

It would hardly please the Know-Nothings to know that Silvio Bedini, a Smithsonian expert who works closely with the Vatican museum in Rome on many projects, has sent color transparencies of the obelisk in hopes of finding out whether it matches any fragment from the long destroyed Temple of Concord that the Vatican might find among its treasure trove. Or that Bedini himself comes from the same family as Cardinal Bedini, founder of the American College of Rome and the first papal nuncio to America, who, he thinks, may have been the one to suggest to Pius IX that he send that missing stone as a tribute to George Washington.