Nothing better becomes the latest version of the Museum of Modern Art than a leisurely stroll through its galleries and public spaces.

The art still comes first, of course. MoMA's nonpareil collection of 20th-century painting and sculpture was largely unavailable for three years during the museum's expansion, and it is good to have it back, as it were, in circulation.

But if a visitor wants to come to terms with the architecture of the new MoMA, to grasp its elusive qualities and experience its subtle excitements, then there is only one thing to do: Walk, slowly, among its rooms, anterooms, corridors and lobbies. Pause when the fancy strikes for a particular view or work of art. Stop at one of the two cafes to rest awhile.

And then, do it all over again.

Movement through these sociable, affecting spaces is the key to appreciating Yoshio Taniguchi's artful architecture, which is so elegantly matter-of-fact when seen from the outside.

Taniguchi, 67, was the eldest among the 10 architects invited seven years ago to compete for the complex, prestigious MoMA commission. Having worked exclusively in Japan, he was not widely known, and his selection surprised many in the architectural world.

Yet it's clear that the MoMA folks knew exactly what they were doing when they put Taniguchi on the list. As if to underline the point, Terence Riley, chief curator of the museum's department of architecture and design, organized an exhibition for the opening titled "Yoshio Taniguchi: Nine Museums."

Documenting eight museum projects in Japan plus the MoMA design, the show demonstrates how, with painstaking intensity, Taniguchi honed his skills over the years. It's almost as if all along he had been preparing for the MoMA prize.

Taniguchi's aesthetic of pure abstraction, developed from the same roots that fed Philip Goodwin and Edward Durrell Stone when they designed the original building on West 53rd Street in the late 1930s, fits the MoMA mission. Unlike some of the other competition entries, Taniguchi's design is not a thing of the moment. Rather, it strongly implies a continuity of modernist architecture.

Equally important, Taniguchi's approach combines sophisticated engineering with place-sensitive design. One can easily spot certain favorite themes in the work, such as a preference for open portico forms on a very large scale, yet each design clearly was created for a specific client in a particular location.

Indeed, the MoMA design is like an enormous, complicated, site-specific sculpture. The museum had grown in increments over the decades, but this time around, Director Glenn Lowry made it clear that the museum did not want just another discrete addition, no matter how distinguished.

Rather, Lowry wrote, if the museum were to meet the challenges of the future, "it had to create a new museum," not only bigger but different. New kinds of spaces and spatial relationships were called for, he emphasized, and it all had to be tied together on the tight midtown Manhattan site. (MoMA had provided the expansion room by purchasing and demolishing an adjacent hotel on 54th Street in the mid-1990s.)

Taniguchi responded with confidence and sophistication. He proposed selective demolition of existing buildings. He designed different facade treatments on the south and north, in accordance with the specific qualities of 53rd and 54th streets. He provided, for the first time, a through connection on the ground floor, with entrances on both streets.

As asked, he provided a variety of spaces for art display -- big, high, columnless spaces for contemporary art; smaller rooms for MoMA's permanent collection of easel-scale paintings and human-scale sculptures, and even more intimate contained galleries for photographs and works on paper.

Furthermore, Taniguchi linked new and reconstituted old spaces by focusing the whole composition on the splendid sculpture garden designed in 1953 by Philip Johnson. And he accounted for all the needed expansion space -- nearly doubling the museum's physical size -- with new buildings both east and west of the sculpture garden.

Thus, the most dramatic exterior changes are visible on 54th Street. To the east of the garden rises a medium-size building for education and research. To the west is the new exhibition wing and, behind that, a new mid-rise tower for administrative offices.

The architect also reshaped the edges of the sculpture garden and rebuilt all of the northern facades -- the back ends of the 53rd Street buildings -- so that the composition reads as a convincing whole. The scene is now quietly impressive. Every surface is crisply sheathed with thin membranes of glass, metal or stone. And two of those Taniguchi porticoes, characteristically huge, face each other across the length of the garden.

On the 53rd Street side Taniguchi preferred to preserve, as he put it, MoMA's "record of regeneration." Thus the iconic white Goodwin-Stone building remains. So does Johnson's elegant steel-and-glass facade of 1964 immediately to the east and, of course, Cesar Pelli's sleek 1984 residential tower to the west, whose lower floors are part of the MoMA complex.

To the west of that, a new Taniguchi facade, in dark reflective glass, completes the composition. Multiple entryways now enliven the street -- there's one for the museum's upscale restaurant, the Modern; the Goodwin-Stone doorway, restored to its original modern curve; the residential entry; MoMA's new main entrance; a door to a spacious new bookstore; and access to museum offices.

All of this exterior work is smart and fairly low-key. Unlike many museums designed from the 1980s onward, this is one you could almost pass by without notice. (It is worth recalling that Taniguchi did his initial design in 1997, the year that the shimmering shapes of Frank Gehry's Bilbao Guggenheim wowed the world.)

The new MoMA is an attractive integrated collection of buildings, each with its own delicately detailed surface. Only by being inside the buildings, however, does one begin to comprehend the degree of integration among them. You learn the new MoMA, and learn to love its architecture, by moving about its interior spaces.

At first, there's almost nothing. From either 53rd or 54th Street you enter a long, wide, rather low-ceilinged blank space with white walls and an attractive slate floor. You buy tickets or make reservations at long black tables made of stone.

It is an oft-used architectural device, of course, to deploy a compressed space as an entryway to a more expansive one. But unlike, say, a medieval cathedral, here the transition is gradual. You can get but a glimpse of great height from this ground-floor corridor. The real impact doesn't hit until after you've ascended a graceful stairwell to the second floor.

There, on a platform shared by "Broken Obelisk," Barnett Newman's mammoth bronze, many first-time visitors will do a 360-degree turn, looking up and around at a tall open space, not easily decipherable despite its 110-foot height. One senses right away that this will be the beginning of a journey with many routes and many surprises.

One senses, too, that Taniguchi has planned it all with the skill of a sensitive choreographer or expert landscape gardener. Throughout the spiraling journey in the six tall floors of the new wing or the lower-ceilinged galleries of the Goodwin-Stone building, the visitor again and again will find himself crossing the central atrium. All paths, eventually, lead to it.

In this, it is very like the atrium of I.M. Pei's 1978 East Building of the National Gallery of Art. In most respects, however, Taniguchi's atrium is a very different sort of place. Unlike Pei's triangulated atrium, for instance, this one is based entirely upon right angles. Nor is it wide open, with almost all points visible from all others. Nor is it bathed in natural light from an astonishing skylight.

Rather, because its configuration differs from floor to floor (except on the fourth and fifth, where it is the same), the space is subtly, or sometimes dramatically, unpredictable. There are six bridges and more than a dozen openings of different sizes cut into its soaring white walls.

In consequence, not only does a visitor repeatedly cross the space during the stroll, he also is constantly looking into it -- down, up or across. The openings vary in dimension, from nine-foot squares, say, to rectangles more than 40 feet tall, and they frame views of artwork and people on different floors. It all makes for an exceedingly pleasing, dynamic (and sometimes even a bit dizzying) spatial experience.

Likewise, openings in the exterior walls are many and carefully calculated. Dazzling views into the garden through glass walls contrast with framed views through tall niches in the architecture. Glass panels with white ceramic frit give an entirely different feel to the outside than do views through the dark tinted glass, which make New York seem a city without sun. The effect, in sum, is to intensify one's awareness of both outside and inside, of architecture, nature and city.

And, it is almost needless to say, the architecture in some way helps to intensify one's experience of the art. That's the aim every time a new museum is built, but it doesn't always work. Happily, it did happen here.

The new MoMA offers dazzling views of the sculpture garden through glass walls, above, and the back ends of the West 53rd Street facade, at right.Cut throughs in the atrium allow views of the art across the museum space. The configuration differs from floor to floor and the space is unpredictable.