It's probably one of the most controversial buildings in Sydney, squatting for decades as a big, brutal presence on the corner of Castlereagh and Goulburn streets, and until now, unfinished. By next month, however, 30 years after it was built, the NSW Masonic Centre will finally be completed with a 24-storey tower that was designed in 1974.

When Nick Lucas, Grocon's head of development for NSW and Queensland, bought the rights to the air space above the Masonic Centre, they came with plans for a contemporary glass curtain-wall tower "but we preferred the original design", he said this week. In fact, said Lucas, "we believe the '70s are back in fashion".

This may be bad news for those who would prefer that the 1970s - and in particular, the "new brutalist" style of architecture which had a brief Sydney heyday in that decade - stayed safely buried. Elizabeth Farrelly, the Herald's architecture critic, once described the Masonic Centre as "one of the least endearing buildings on Earth ... no one has ever loved it, nor ever will". Many agreed.

Even those most deeply committed to the architecture of the 20th century can be ambivalent. Jacqueline Urford, who chairs the heritage committee of the Royal Australian Institute of Architects, says this is "most brutal of the brutalist buildings", adding that "I admire it because it stands for what it is - but I can't say I love it".

But Dr Harry Margalit, an architecture lecturer at the University of Sydney, differs. "Without doubt there will come a time when it is loved, and I think that time is not far away," he says. He also says it could be listed as "a companion piece to the Opera House, one which illuminates the evolution of architectural ideas both in Sydney and abroad". On a national ranking, he says, "its overall significance ... is of the highest order".

Andrew Andersons, of PTW, the architects carrying out the original Joseland Gilling plans for the tower, agrees. Aware of the original Max Dupain photographs (two of which are reproduced here), he says that "it's not an ugly building; it's just an unfinished building" and it makes "a big sculptural contribution to the street".

For whatever reason - good or bad - it's a building few people can ignore. In Urford's words, "you can't say it does anything meekly" and it belongs in a series built in Sydney from the '70s to the early '80s that includes the Supreme Court and the Elizabeth Street law school, the Sydney Water building on Bathurst Street, Sydney University's Wentworth Building on City Road, the Warringah Civic Centre in Dee Why and the UTS campus at Ku-ring-gai.

In Canberra, the High Court and the National Gallery made their very firm marks while in Perth, Margalit says, there is "a wonderful collection [of brutalist buildings], some of the best in the world" including "almost the whole of the Curtin University campus, some buildings downtown and a string of mainly government buildings along the shore".

THE brutalist movement had begun in England in the '50s, led by Peter and Alison Smithson, but did not percolate through to Australia until much later, with Joseland Gilling producing the Masonic Centre (and the Qantas building near Wynyard). In the same era the Government Architect's office produced the Ku-ring-gai campus while Edwards Madigan designed the Warringah Civic Centre, which Urford says was virtually a prototype for the High Court in Canberra.

Margalit says: "These buildings will not come again; for one thing, they would be too expensive to build now. They were built in the negative - by pouring concrete in the form, then stripping it away. So to build a spiral stair in concrete, as they did at the Masonic Centre - well, that sort of work takes a long time to put together.

"The quality of the construction is extraordinary; the tolerances are incredibly fine; it's beautifully made. And very few buildings can match its interior quality" - an opinion with which Andersons concurs, adding that it has been "beautifully maintained and is in perfect condition". His firm's work on completing the centre has been "a chance to regain an icon that was almost lost", a "rescue mission ... for one of Sydney's most remarkable sites".

It has been luckier than some of its companion buildings are likely to be. The Warringah centre has been earmarked as the site for a new hospital while at Ku-ring-gai, UTS has decided to vacate its Sulman-award winning building, leaving it and its site up for grabs. Ian de Vulder, a former Ku-ring-gai councillor, says a significant feature of the complex is "the way it used the whole landscape and melded the buildings into it", which is also at risk if the site is redeveloped.

A striking feature of the Ku-ring-gai building is its large, top-lit internal street - an element Margalit traces to the "social program" of these buildings. "It's the generous circulation spaces that were designed to make them sociable buildings, with places for people to gather: at UTS Ku-ring-gai, it's that internal street; the Wilkinson building has generous spaces around its stairs; there's the enormous foyer between the two halls at the Masonic Centre and UTS Broadway also has a fantastic foyer, though the tower itself is not so good," he says.

"There was a certain brutal honesty about materials in concert with concern for creating social spaces. It's as if they were saying it's no good having a pretty building with no heart."