NEW YORK -- Since the day they were done 90 years ago, the copper-helmeted turrets of the Main Building on Ellis Island have shimmered in the distance like beacons misplaced from Venice or Byzantium.

Today, however, they attract the eye with new brilliance, as does, in fact, every aspect of the Main Building. Left to go to ruin in 1954, the building has been treated to a first-class renovation that has taken eight years to accomplish. It will be officially dedicated on Sunday (and opened to the public on Monday) as a museum of immigration.

Ellis Island, of course, was the principal entry point for immigrants to the United States from 1892 to 1924, when more than 12 million people passed though the main building. Fittingly, visitors to the museum will disembark from ferries at precisely the place where for many years immigrants ended their transatlantic journey. Demographers say that about 40 percent of the country's population today can trace roots to this gateway.

Today, as formerly, the sighting of Ellis Island stirs ambivalent emotions. Approximately 2 percent of those who made the voyage during the island's years of active use as an immigration center were turned back for medical, economic and political reasons. And up until its closing in 1954 the Main Building continued to serve as a center for deportations.

Hence, this highly visible 27.5-acre spot of land in the lower Hudson River, formed mainly of compacted rocky soil from the construction of New York's subway system and supporting 33 institutional buildings, is willy-nilly a potent symbol. The ground remains at once hallowed and haunted -- it's the "Golden Door" and also the "Island of Tears."

Despite this ambivalence -- or perhaps even because of it -- the reopening of the Main Building as a museum is basically something to cheer about. In the 1950s its owner, the federal government, tried to sell the island, albeit lackadaisically. There were plenty of takers, though none offered what the government considered a fair price.

In her history of the island, "Strangers at the Door," Ann Novotny listed the following proposals: luxury hotel development, private mansion, orphanage, narcotics treatment center, gambling casino, university, Bible college, boys' town, hospital, veterans' rest camp, amusement park, prison, housing for the elderly, seamen's school, world trade fair site. Frank Lloyd Wright conceived a "perfect city of tomorrow" for the island. Philip Johnson proposed stabilizing the principal buildings as "instant ruins" to set off a mammoth memorial wall bearing the engraved names of immigrants.

Considering this history, the decision to save the island as a "national historical site," which dates back to the mid-'60s, seems oh so sensible. The $156 million refurbishment, though limited in scope, follows from that decision. Funded by private donations to the Statue of Liberty-Ellis Island Foundation, the effort focuses on the Main Building, leaving unsettled the fate of the other buildings, most located on the southern portion of the island and all in sorry shape.

This is true even though the refurbishment project did include the nearby Powerhouse, which has been repaired and refitted with boilers capable of supplying energy to the entire island. The island's caretaker, the National Park Service, appears determined to save as many of the buildings as possible and to maintain the basic institutional layout.

But the Park Service has no money to undertake so imposing a task and, in any case, no legitimate idea as to how this very large ensemble might be put to public use. Officials talk of a conference center; so far, negotiations with a private nonprofit company (the Center for Housing Partnerships) have produced no apparent result.

But the Main Building in itself forms an evocative, if often chilling, testament to its principal historic use. Designed by the little-remembered New York firm of Boring & Tilton and completed in 1900, it's a pompously pretty red-brick and stone structure. Characteristically for the period, the architects used Beaux-Arts ornamentation to make symbolic points. From close up, one notices just how stern are the giant sculpted eagles atop rusticated pilasters, and how impervious are the blind-eyed allegorical heads doing double duty as keystones in the immense arched openings of the facade.

One doubts, however, that incoming steerage passengers, having just shipped by the memorable Statue of Liberty, had any time or care to ponder the fine points of the symbolism or this architecture. They were herded rather quickly from the dock to the building's interior, which indeed was, as noted by John Belle, one of the principal restoration architects, an "extremely efficient machine for moving people." Despite overcrowding -- more than 11,000 people were processed on the peak day in 1907 -- it took an average of about five hours for each person to pass through the building.

Technically, restoring this building was a demanding job. For instance, it took more than two years simply to dry out a structure badly damaged by prolonged exposure to the elements, a process that involved using large heaters outside the building, pressurized dry air inside, and gradual release of moisture through big collapsible ducts. Reproducing the peculiar matte-tan texture of the interior Caen stone (an artificial surface much used at the turn of the century) required many trials. Even cleaning the facades with low-pressure steam proved difficult and time-consuming.

Philosophically, however, the task as conceived was quite straightforward. Both client and restoration architects (the National Park Service and the firms of Beyer Blinder Belle and Notter Finegold + Alexander, respectively) had the great good sense to tamper as little as possible with the basics of the building. Where additions were deemed absolutely necessary, members of the restoration team did not fiddle with Williamsburg-like re-creations, nor did they beat their breasts in search of startling contrast. Rather, they designed things that simply acknowledge their newness.

The mainly felicitous results begin on the outside, where the old steel-and-glass entrance canopy (razed in 1932) was done over in a frankly contemporary version. Constructed on the old, 114-foot-long footprint, it evokes the original even though it has a great deal more glass -- the added transparency seems fitting to the new function, which is less to shelter or to herd than to open the eyes of visitors no longer preoccupied by the old anxieties.

Likewise, the new staircase leading from the ground-floor baggage room to the Registry Room on the second floor is a crisp, modern design following exactly the form of the old, long-gone stairwell. At first, the low-key design seems upsetting -- this was, after all, a dramatic point of the whole, wrenching passage through the building, and many a moving tale was told of cursory medical tests conducted by examiners ranged along the topmost railing. But after a while this matter-of-factness makes its telling point.

The definitive centerpiece of the building is the Registry Room, a vast, vaulted chamber where tired people waited to learn the answer at the end of their voyage: in or out. Lines started at one end of the room, by the stairwell, and progressed to the other, where tables for immigration officials were arrayed. As restored, the room is impossibly spick-and-span -- the light levels are high, the herringbone tiled ceiling sparkles -- but wisely it has been only minimally furnished.

Obviously, the quality of the exhibits will have a great deal to do with one's experience of the place; when I visited the building last month, installation was just beginning. It was encouraging to learn, however, from Park Service specialist Diana Pardue, that the idea is to avoid an all-too-familiar, celebratory accounting of the immigrants' passage through the Golden Door. Instead, the focus will be upon the actual complexity of the experience.

Assembled, designed and constructed by a consortium consisting of the three New York firms Metaform, Rathe Productions, and Design and Production Inc., the exhibits will comprise more than 2,000 artifacts and 1,500 photographs referring mainly to the history of Ellis Island's transient population and also taking on the wider subject of immigration throughout the country's history.

The architectural table has been well set for such a serving -- without overmuch disturbing the original floor plan, the architects determined to install most of the museum displays in the building's symmetrical wings. By covering a light well, formerly open to the sky, with a glass roof, they were able to reclaim sufficient space for circulation; they also were able to squeeze in two commodious theaters.

This is a sensitive arrangement. In contrast to the size and architectural clarity of the central chambers, the building's wings are labyrinthine. It is when wandering through the many rooms on either side of the main halls -- many containing exhibits but many left more or less as they were, with bunk beds, say, or washable tile walls and here and there a few splotches of scientifically preserved graffiti -- that one begins more tangibly to sense the enormity of the enterprise, of the befuddling bureaucracy and the human-scale defeats and victories played out on the island. From these quarters one returns to the Registry Room with fresh insight -- its spaciousness and emptiness stimulate the imagination. One wants to linger in this hall.