Architecture: Extension of a New York controversy: The Guggenheim is no ordinary museum. Ultan Guilfoyle looks at the legacy of Frank Lloyd Wright

Woody Allen says it looks like a giant lavatory basin. Jackie Onassis agrees. Thirty-three years after Frank Lloyd Wright completed his Guggenheim Museum, the building continues to be New York's most controversial. The functional 10- storey extension that opened last month is only the latest chapter in the story of a building that has made friends and enemies in equal numbers.

During its construction, Wright was accused of designing a building that was architecture for architecture's sake. This huge inverted concrete snail's shell, with its quarter mile of internal ramps from which to view sculpture and paintings was, some critics said, the finest artwork in the massive Guggenheim collection, but not much good for displaying the works of other artists. There is an old saying about the Guggenheim; you come to see Kandinsky or Picasso, but you stay to see Frank Lloyd Wright.

When Thomas Krens, the museum's dynamic new curator, commissioned Gwathmey Siegel & Associates to restore the gallery and to add an extension that would cater for the functional needs of the building, he was bound to make new enemies. The public had grown fond of Wright's folly; there was widespread feeling that, no matter how clean-cut and simple, any addition to Wright's building was a scandal.

Wright had been a highly controversial choice when the museum was mooted. The first director of the Guggenheim, the German-born Baroness Hilla von Rebay, had persuaded her patron, Solomon Guggenheim, to commission Wright to build a museum to house the collection of Modern art, including works by Kandinsky, Mondrian and Moholy-Nagy, which she had built up for him.

But Guggenheim died shortly before the museum opened in 1959 and Rebay was replaced by James Johnson Sweeney, a highly respected professional museum curator and a Modernist in the contemporary clean-cut Philip Johnson or Ludwig Mies van der Rohe vein. He hated Wright's organic design and disliked Wright himself, feeling that he was inheriting an unworkable building. Apart from the lack of storage space, conservation rooms and offices, visitors had to stand on an uncomfortable slope on the otherwise beautiful ramp of the gallery to look at the artworks. In the sixth months following Wright's death - also in 1959 - Sweeney forced through crude functional changes which have only now been set right in Krens' dollars 54.9m (pounds 28.7m) renovation and extension.

The public, however, appeared to like the building from the start. They poked fun, but this was more affection than criticism. A typical cartoon from the New Yorker showed two fat and be-furred Upper East Side ladies accosting a mounted policeman in front of the building. 'Say officer, are they allowed do that on Fifth Avenue?'

The experience of walking into the Guggenheim, mind-boggling even in this age of super-stimulation, must have been shocking in 1959. Sir Richard Rogers, filming in the Guggenheim for the South Bank Show a fortnight ago, described entering it as 'one of the most wonderful and impressive moments one can imagine'.

'You can think of the Guggenheim as a piazza on the ground floor,' says Rogers 'with a street which winds up a hillside, round and round until you get to the top.' The Guggenheim will be further enhanced when the restaurant and auditorium underneath the gallery - reached by a ramp from Fifth Avenue - open later this year; these have long been annexed by the museum's staff, who now have their own space.

Members of the artistic community were, and still are, divided. Perhaps this is because they knew or remember that Wright cared little for studio art. A group of artists led by Robert Motherwell and Willem de Kooning had protested against the design, but Wright was characteristically dismissive.

Dan Flavin, the sculptor whose installation opened the restored building last month, worked in the building when new. 'I was working in the mailroom as a messenger and I saw what Sweeney went through to present paintings here. They are difficult quarters for painters.'

'The building asserts itself with great force,' says Thomas Messer, a former director of the Guggenheim. 'If one doesn't succeed, the building shows off the work negatively, and if one does succeed, the building takes the credit.'

There are those in New York who say that Wright designed his building as an asymmetric nose-thumbing at the rigid order of New York's streets and architecture. This is simply not true. Philip Johnson, a harsh critic of Wright in the Fifties, sat on a camera box in the Guggenheim a fortnight ago and said: 'Frankie was a very strange man, but he always had this dream of a spiral, of a building that would spring up. This was the first time he got the chance and it is a beautiful job, one of the very great rooms in the world.' Wright affected a hatred for New York, says Johnson, but this was just a typical 'Frankie posture . . . he had a sneaky affection for it.'

By the mid-Eighties, the building had fallen into a sad state. 'There was chicken wire where the light now streams in, with bits of the lighting blocked off to stop it hitting the paintings,' says Rogers. When Tom Krens succeeded Thomas Messer as museum director in 1988, a programme of expansion and restoration had just begun. With a pugnacious zeal worthy of Wright himself, Krens quickly decided, with the architect Charles Gwathmey, to bring the Wright building back fully to its former glory.

'What we tried to do with the restoration,' says Krens 'was simply to 'unpack' the building, to take it back to what we call its 'pre-original' condition.' To make it, in other words, the building it was always meant to be, although Wright would surely have disapproved of the dazzling white paint on the outside of the old gallery; he used a subdued sandy colour.

Compared to the soaring beauty of the spiral gallery, the slender new wing (almost doubling exhibition space with its three double-height galleries), with its tartan-patterned wall of gray limestone, stands a little shyly against Wright's curves, but this does not, as some people suggest, lessen the impact of the Wright building. The relationship of the new wing to the old rotunda was central to Gwathmey's design; he has treated the limestone in such a way that it will darken in time, emphasising the contrast between the old and the new.

The renovation of the building has also opened up Wright's smaller 'Monitor' building, as it is called, alongside the spiralling main gallery. With its lozenge shapes, curved metal windows and sculpture terrace, the Guggenheim engages visitors in a whole new set of architectural and artistic experiences.

Perhaps the most striking aspect of the remodelled Guggenheim, however, is the way that Krens has approached the relationship between the art on show and the artistry of the building. 'Museums are fundamentally an 18th-century conception realised in a 19th-century box. Wright very clearly was interested in putting the museum into the 21st century by completely defying the notion of a box.'

Having chosen to launch the 'unpacked' Guggenheim with a breathtaking coloured neon sculpture by Flavin, specifically designed for the building, Krens points the way forward. And it works. Flavin's sculpture engages the Wright building directly. With a tower of pink neon rising from the centre of the rotunda floor to the glass dome some 70ft above it, and a ribbon of fluorescent tubes negotiating the individual bays all the way up the ramp, Flavin shows how artists can tackle Wright's domineering architecture.

Krens is now taking the Guggenheim outside Wright's concrete snail. The new SoHo Guggenheim, New York, opens soon (designed by the Irata Isozaki, the Japanese architect) and outposts of the Guggenheim are scheduled to open in Bilbao (Frank Gehry is designing the building) and Salzburg (Hans Hollein) in the next few years. In Venice, there are plans for the Guggenheim to take over the old Customs House building, a few hundred yards from the existing Peggy Guggenheim collection.

Frank Lloyd Wright said, rather grandly, that 'if you want to experience man, to know him, go into his buildings'. Going into the Guggenheim Museum, with its inspirational spaces, complex geometries, shifting plays of light and shade, you get the sense that Wright must have been some man to know.

The writer is producer of a film, directed by Peter Lydon, on Frank Lloyd Wright and the Guggenheim Museum to be shown on the 'South Bank Show'.

(Photographs omitted)