There have been black people on the streets of Venice for centuries.

Art used to take some slight account of them. Maybe it can once again.

That simple idea of carefully noticed blackness is a central theme in "Speak of Me as I Am," a new show by Bronx-born artist Fred Wilson. It fills the American Pavilion at this year's Venice Biennale International Art Exhibition, opening Sunday to an expectant public now pouring into Venice from all over.

The Biennale is the world's oldest and most prestigious roundup of contemporary art, celebrating its 50th edition this year with an unusually massive spread. On top of the 300 or so artists invited to group shows by Biennale organizers, 32 nations have their own pavilions scattered across the festival park, with the American Pavilion -- the size of a small mansion -- filling a choice lot in the middle of them all. For decades now that pavilion's been a special focus of attention, and Wilson's new work seems set to keep it in the thick of things: At Thursday's thronging media preview, the U.S. pavilion was about the only one that had to practice crowd control.

(It didn't hurt that in intolerable summer temperatures, even for Italy, Wilson's galleries were air-conditioned to nearly American standards.)

Wilson's contribution to the Biennale starts making an impact even before you've walked through the pavilion doors. The portico of the building has always had four fluted columns holding it up, but between two of those classically white pillars Wilson has hung banners depicting giant black men, dressed in fancy-looking Renaissance rags, who seem to bear some of the roof's weight upon their shoulders. There could be a distinctly American message here -- that the shining glory of U.S. wealth depends on an unacknowledged history of black slaves who helped to build and shore up that wealth. But there's one hitch in such a reading: Wilson's black eaves-bearers are famously Venetian, cribbed from giant marble statues on one of the most lavish of baroque tombs. Issues of black and white may be central to American history, society and identity, but it turns out the United States has never had a monopoly on troubled race relations.

Go inside the pavilion, and you see Wilson's attempt to take a closer look at how blacks have fit into the Venetian scheme of things over the years, even until now.

His is a very rare Biennale project that takes into account the city all around it.

The best room in the show by far is also by far the most straightforward. On one wall, Wilson has hung three borrowed Old Master oil paintings, so as to hint at how frequently blacks are featured in some of the classics of Western art, even though we don't tend to pay their presence much attention: One 18th-century painting includes a black youth as a servant to King David; a Renaissance work shows the goddess Diana with a black among her nymphs; a third painting, again from the 16th century, is of a Medici prince who may have been part black.

On another wall, a bunch of snapshots from museums show details of other views of blacks in Renaissance Italian art: A black Wise Man from a famous Nativity scene; blacks as fancily dressed servants at fantastical biblical feasts; blacks as gondoliers and porters seen in views of Venice. Most of the figures in these pictures may be servants, and perhaps were included for their exoticism, but they aren't caricatures, yet. They don't fit into stereotypes about blackness, because such stereotypes had yet to jell. In the Renaissance, blacks seem to have been a normal element in the exotic mix of cosmopolitan Venice -- they were far from becoming Sambo or Uncle Tom.

Newer records of Venetian blackness don't fare so well.

A glass case in Wilson's show presents some standard goods out of today's local stores: A box of "Othello" chocolates; a big, dark-chocolate cookie called "Moor's bread" (the pale-colored version is, of course, called "Doge's Bread"); fancy golden earrings with "Moor's heads" dangling from them.

A photograph blown up nearby shows a typical local shop window full of high-end Venetian kitsch -- with a strong concentration on elaborately costumed blacks carved in wood or cast in plaster, then garishly painted and gilded. Scattered across the show are actual examples of such objects, bought by Wilson during Venetian stays over the last year or so: Little candle-holding Moors in glass; a boy-size standing Moor meant to hold a tray, for presenting business cards or appetizers; Moors holding candelabra, copied from beloved figures in the old La Fenice opera house. They're not far from the notorious lawn jockeys once popular in the United States, except that most people over here never seem to give a second thought to what these objects might signify to any modern black.

And finally, on the same wall as the photographic details from Renaissance art are snapshots of real black people treading the pavements of Venice. A few look like tourists. Most are unlicensed African migrants hawking fake-tribal trinkets and counterfeit Hermes bags, hated by tax-paying store owners and kept on the move by the police. (Wilson has set up his own version of such a street-side stall alongside the pavilion. But he's replaced the usual purses knocked off in Hong Kong with deluxe bags of his own design; they will sell for high art-object prices once this show comes down.) Italy's African peddlers represent about the lowest stratum in its society, no longer considered people truly exotic and interesting and worth rendering in art, as they were in the Renaissance, but now only worth ignoring, unless they get so much in the way that they become a problem to be solved.

At its best, Wilson's art acts like a kind of anthropological survey of where blackness has fit and now fits into our cultures, both high and low. Or you can think of Wilson as working like a documentary photographer, not altering the world, as many artists do, but simply presenting unnoticed aspects of it to us. This repositioning and rethinking of objects from the past is what earned Wilson his reputation, starting with a solo show that came to the Washington Project for the Arts in 1991, followed by a famous show in 1992 in Baltimore and then others at important venues all around the world.

Unfortunately, some of his new work in Venice has become much less direct, and therefore less compelling: He takes the strong evidence he's gathered, and dilutes it with a heavy dose of artiness. A standing black figure is turned into evident, self-conscious "art" by having its head replaced with a globe. Another one has a chessboard painted onto its serving tray; all the white chess pieces have been removed, while the black ones now lie scattered. Approach one of those borrowed Old Master paintings, and you trigger a portentous recording of the words "I am you and the others, too," spoken in a half-dozen different languages.

All this weighty allegory -- or maybe it's surrealism lite -- is meant to tell us that this is important art to which attention must be paid. But in the best of Wilson's work, it's not fussy artifice that makes it matter. It's the complex reality that we gain access to.

The Venice Biennale runs until Nov. 2. Visit www.labiennale.org.

At the entrance to the American Pavilion, Wilson makes his point early.