NEW YORK - The late Philadelphia architect Louis I. Kahn wasn't the type to turn out quickie, throwaway designs. Maybe that explains why so few of his projects were built. He spent his career trying to conjure up structures with the universal quality of a Greek temple, that spoke across generations, that were capable of lasting an eternity.

Wednesday, four decades after Kahn was found dead of a heart attack in Penn Station's men's room, New York officials will dedicate a work he designed in 1974, a memorial to President Franklin D. Roosevelt called Four Freedoms Park.

Situated on Roosevelt Island in New York's East River, the park is as pure a distillation of his architectural philosophy as you can imagine, assembled from little more than stone, earth, sky and water. With its sparkling white stone and long vista, it expresses something few contemporary memorials would dare to suggest: confidence in the future.

Posthumous architecture rarely ends well. This work succeeds because the project team treated Four Freedoms like the construction of a Renaissance church. During the long years that it took for the undertaking to gestate, Kahn's vision and values were transmitted intact from generation to generation, even though the people who completed it - project manager Gina Pollara and Mitchell/Giurgola Architects - never met its designer.

The park manages to be many things at once. It is, first of all, a memorial to Roosevelt and the values he articulated at the start of World War II in his famous "Four Freedoms" speech, asserting America's commitment to freedom, tolerance, peace, and prosperity for all.

But it is equally a statement about architecture and its special power to say more than can be put into words. Kahn exploits the memorial's location to offer insights about the interdependency of civilization and nature that are as relevant today as they were in the '70s. The quiet, minimalist design also promises to be a usable public space where people can enjoy a picnic or concert and reconnect with New York's island origins.

Until the last few years, however, few harbored much hope that Kahn's design would ever move from the yellowed tracing paper, marked up at his Philadelphia office at 15th and Walnut Streets, to physical form at the southern tip of Roosevelt Island.

The memorial to the 32d president was derailed after Kahn's death at 73, first by New York City's near-bankruptcy in 1975, then by a state fiscal crisis, and later by the Reagan-era repudiation of Roosevelt's world view. At one point, the site, with its wide-angle views of Manhattan's East Side, was nearly lost to a Marriott hotel project.

The election of President Obama, in the midst of the worst economic crisis since the Great Depression, rekindled interest in the author of the New Deal. Seizing the moment, William J. vanden Heuvel, a former U.S. ambassador who is devoted to preserving Roosevelt's legacy, managed to raise $53 million for the memorial, much of it from donors.

That huge sum was spent on a work of deceptive simplicity. Triangular in shape, Four Freedoms Park follows the contours of the island and juts into the river like the prow of a ship.

At the very tip, Kahn fashioned a spare outdoor room from 12-foot blocks of white granite dotted with black specks. The room is meant to serve as a place of contemplation by isolating the visitor from the world. Only the fourth wall has been left open. It frames a view of a rocky outcrop, the swirling river and, in the distance, the polished tower of the United Nations, which Roosevelt helped found.

To get to this point, you must leave behind the churning bustle of Manhattan and travel across the water by tram or subway to a sliver of rock once named Welfare Island because it was where prisoners, smallpox victims, and "lunatics" were dispatched. It's only a short walk from the tram station to land's end, yet the city quickly recedes like a memory.

Memorials are often structured as journeys through space. Kahn, who designed the park with the landscape architect Harriet Pattison (the mother of his son, Nathaniel), wanted this one to reveal itself slowly. So when you arrive, the first thing you see is not the impressive view or the city skyline, but a monumental staircase. You begin the journey either by climbing these steps or ascending the gently sloping ramps that run along the edges of the park. In tribute to Roosevelt, who relied on a wheelchair for many years of his life, accessibility is embedded in the design.

At the top of the main platform, a wedge of lawn unfurls, bounded by allées of trees pruned into teardrop canopies. The two rows of trees converge in a point on the horizon line, drawing the eyes to the end of the island. Gazing toward the water, you see a huge head of Roosevelt, by the sculptor Jo Davidson, resting in the niche of a stone wall.

At its most basic, Four Freedoms Park is a study in perspective. It can been seen as the East Coast corollary of Kahn's Salk Institute in California, which enlists views of the sky and sea as major features of the composition.

But Four Freedoms employs a more complex and refined geometry than Salk. At the same time that the memorial's side paths ramp up, the lawn ramps down. The result is a complex arrangement of angles that become a stage for plays of light and shadow. This design is clearly not as simple as it first appears.

Kahn wasn't religious in a formal way, but he had a deeply spiritual bent. He uses geometry the way Renaissance architects like Michelangelo and Bernini did, to celebrate the perfection of a higher power. Consider the numbers: The stairs are 12 feet above the entry plaza. The outdoor room's granite blocks are 12 feet high. The room is 60 feet square, or 12 by 5.

Kahn, who was famous for his aphorisms, liked to say that "the room is the beginning of architecture." Given that architecture marks the beginning of civilization, the decision to make the room the final destination is heavy with biblical symbolism. To reach it, you must first walk through the garden.

Compared with some recent memorials, like the World War II memorial in Washington, Kahn's design is stunningly quiet. Some details are just barely perceptible. For instance, Kahn specified that the room's granite blocks should be given a rough, saw-cut surface on the outer sides. But in the inch-wide slit separating the stones, they are polished. The mirrored surface captures light in a magical way. In offering teasing glimpses of the city, the slits act like portals back to the world.

Nearly 40 years after Kahn imagined Four Freedoms Park, it is remarkable that it is still possible to discover new meanings in the design. It's a strong sign that this is architecture that will not grow old.