Little is now known about the two intrepid thieves who, costumed as policemen, robbed Isabella Stewart Gardner's remarkable Boston museum early Sunday morning of a dozen works of art. But a list of what they stole leads one to suspect that perhaps the robbers were as eccentric as was she.

The late Mrs. Gardner (1840-1924) was a most peculiar soul. She liked to shock her neighbors by promenading Tremont Street led by her pet lion, Rex, on a leather leash. She claimed descent from Mary Stuart, and Robert the Bruce of Scotland, yet swigged beer like a navvy. Sometimes, when holding parties at her home on Beacon Street, she chose to greet her guests not at the front door, but perched high in a tree. Both extravagant and stingy, she underfed her house guests and kept them in near darkness (to save pennies on the gas), and had two enormous diamonds mounted on gold wires so that they waved about her head, in the words of one observer, "like the antennae of a butterfly." While building Fenway Court -- the faux Venetian palace in which she placed her art -- she would wander through its galleries accompanied by a trumpeter employed to summon workmen, one note for the architect, a second for the plumber. She would sometimes heft an ax to hew its thick wood beams.

A seal she designed is set into the wall there. It bears a phoenix rising, a symbol of immortality, and the motto "c'est mon plaisir," a punning phrase which means "it is my pleasure," or "my whim."

The thieves' choices too were whimsical. They took a dozen objects -- major works by masters and minor works as well, pieces large and small. They hit three different galleries. They spent perhaps two hours inside the museum. When one considers what they left behind, a list of what they took makes no sense at all.

The two grandest things they chose -- "The Concert," a 28 1/2-by-25 1/2-inch canvas of 1665-66 by Jan Vermeer of Delft, and "The Storm on the Sea of Galilee" of 1633, an even larger Rembrandt -- are known to every student of Northern European art. Vermeers are so scarce (less than 35 survive) and the Rembrandt is so special (it is his only seascape), that these two works alone, if auctioned off legitimately, might easily fetch as much as $100 million together. But stolen masterworks so famous are near impossible to sell.

They took another Rembrandt oil, "A Lady and Gentleman in Black" of 1633, an early double portrait that is more than four feet high, and a fine, dramatic canvas of 1638, the "Landscape with Obelisk," that, until 1981, was thought to be a major Rembandt, but since has been assigned to his far less famous student, the painter Govaert Flinck.

Were the robbers fooled by its phony Rembrandt signature? It's impossible to say.

The robbers' French selections are equally improbable. They bypassed a Degas oil in favor of a quartet of his works on paper. They also took a small Edouard Manet oil -- "At Tortoni's," an 1878 cafe scene that is but 10 inches high -- and an ancient Chinese bronze.

"All in all," said Arthur K. Wheelock Jr., curator of Northern European baroque painting at the National Gallery of Art, "it is an unbelievable group."

The oddest thing about the robbers' 12-work list is what it omits. Mrs. Gardner, often aided in her choices by art scout Bernard Berenson, specialized in buying Italian works of art. Her remarkable museum, with its marble fireplaces, candelabra, carved furniture, and walls of silk brocade, incorporates various chunks of a 15th-century Venetian palace that she had had dismantled and shipped, in bits, to Boston. Her institution is best known for its extraordinary Renaissance paintings, among them works by Raphael, Fra Angelico and Botticelli. Her amazing Titian, "The Rape of Europa," must rank among the grandest paintings in America. And yet all of these Italian works were somehow left behind.

Some who know the Gardner well, for instance scholar Anne Higonnet, who teaches art history at Wellesley, contends that the thieves were "exceptionally clever" in mixing works too grand to sell with others that, because less well known, might be slipped onto the market. But her point may be debated. Those who steal masterworks are often given credit for subtlety of motive, and for cunning knowledge of the market, that they do not deserve.

Whenever mighty masterworks are stolen from museums, a mighty master criminal is seen behind the theft. Sunday's was no exception. "The art treasures seized from the Isabel Stewart Gardner Museum yesterday were probably contracted for in advance by a black-market collector outside the country, private investigators and art experts theorized yesterday," announced the front page of the Boston Globe.

Such criminal connoisseurs are stock figures in fiction. Jules Verne's Captain Nemo filled his submarine with wondrous stolen pictures. James Bond, while stalking Dr. No on film, stopped to gape in wonder at Goya's "Duke of Wellington" -- which had vanished, in the real world, from London's National Gallery in 1961. In "The Eiger Sanction," Clint Eastwood, the assassin, stocked his hideaway with Pissarros. Because posters from museums are easily obtained set-designers' props, television cop shows often show us masterworks displayed in gilded frames in the mafiosi's lairs.

The legend of the crooked connoisseur has been setting spines atingle for most of the past century. His existence, like that of the Loch Ness monster, is not easily disproved, but no one's caught him yet. FBI agent J. Martial Ribichaud, a specialist in art theft, has said "of course, I've heard such stories. And that's what they are, stories. There is nothing in our files to indicate that such a collector with a private museum has ever been apprehended. It's fiction. It's romance."

There are three possible motives for a theft as chilling as that of the Gardner's priceless Vermeer. The first, and most likely, is to hold the work for ransom with the expectation that the museum's champions will eventually agree to pay. The second possible motive is for anticipated resale, though, if history is any guide, a multimillion-dollar price for that Vermeer, or even a multi-thousand dollar price, is exceedingly unlikely, for who would buy a picture that they could never show? The third is publicity.

Goya's "Duke of Wellington" was stolen not by Dr. No, nor by his mean minions. It was taken by one Kempton Bunton, who'd seized it to protest the British government's refusal to exempt old-age pensioners from television-set license fees. The thief who stole a panel, not yet recovered, from Jan van Eyck's Ghent Alterpiece in 1934 left behind a note protesting the Treaty of Versailles. In Ireland, in 1974, when operatives of the IRA stole 19 precious pictures, among them a Vermeer, from Sir Alfred Beit, one of them exclaimed "capitalist pigs! You're walking on the working class" as he pistol whipped the collector. Though the Beit Vermeer was soon recovered, it has since been stolen once again.

Some works simply vanish. Claude Monet's "Impression Sunrise," the canvas from which Impressionism took its name, was one of nine pictures seized by five armed men from the Marmottan Museum, Paris, in 1985. It has yet to be recovered. Comforting as it may be to imagine that Monet in some master criminal's museum, it is in fact as likely that it has been destroyed.

"The greatest horror," scholar Peter Sutton of the Boston Museum of Fine Arts told the Boston Globe, is that such stolen masterworks have been damaged by their thieves. Sutton mentioned a Raphael madonna on wood panel that was broken in half, and Vermeer's "The Letter," which after being stolen from the Rijksmuseum, Amsterdam, was taken from its stretcher, rolled, and then sat on during a taxi ride. Though eventually retrieved, and painstakingly restored, it will never be the same.

There is as yet no word that the Gardner Rembrandt, or its grand Vermeer, were cut out of their frames. Though Gardner curator Karen Haas yesterday declined to discuss exactly what damage may have been done to the objects during the robbery, she did acknowledge that "most of them were removed intact."

Half in shadow in the foreground of "The Concert" of Vermeer is a table holding instruments and an Oriental rug. The black-and-white checked floor tiles lead the viewer's eye step-by-step into the background, where two women and a man are serenely making music in harmonious silver light. Rembrandt's "Storm" shows Jesus just awakened by his alarmed apostles as a fierce dramatic sea crashes round their boat.

Mrs. Gardner in her will insisted that her home/museum (she lived there more than 20 years after opening it to the public in 1903) be left just as she loved it. There was nothing to be added, and nothing put away. The heavy carved wood chests, the rich brocaded walls, and the hangings of her pictures were to remain unchanged forever. Except, perhaps, for New York's Frick, her beloved Fenway Court is our nation's greatest ornate house museum. The Gardner without its Vermeer is like a smile with a missing tooth. No one can yet say what the thieves intend to do with the objects they have stolen. But they've already done great damage to one of America's finest, most eccentric, most individual works of art.