* Putin to attend opening of $700-million theatre
* Mariinsky is headed by leading world conductor
* Russia aims to make it a major cultural landmark
By Liza Dobkina
ST PETERSBURG, Russia, May 1 (Reuters) - It has been variously described as a sleek piece of modernism or an ugly shopping centre, but whatever Russians think of the exterior of St Petersburg's new Mariinsky Theatre, they will finally get to see inside the much-debated building at its grand opening on Thursday.
President Vladimir Putin will lead a select crowd of guests to the first performance at Mariinsky II, a 2,000-seat theatre, which, at a cost of $700 million, ranks among the most expensive cultural projects ever built.
The new building stands near the 19th century Mariinsky Theatre, one of the great showcases of Russian culture and which became home to the opera and ballet companies renowned around the world under their Soviet-era name of Kirov.
But the new theatre has divided opinion in Putin's home town, where critics have dubbed the glass-and-limestone building the "Mariinsky mall", incongruous among the other elegant 19th-century buildings in the Imperial capital and the ugly sister of its ornately gilded predecessor.
Valery Gergiev, head of the project and regarded by many as the greatest living orchestral conductor, has promoted the plan to build a new Mariinsky for 10 years, capitalising on Putin's desire to show that Russia no longer lags behind the West.
He has promised that doubters will eat their words when they see the interior of the 80,000-square-feet (7,400-square-metre) structure.
"The inauguration of Mariinsky II will reaffirm and strengthen the great tradition of the theatre, opening the way for the future when it will be possible to create cutting-edge works of art and innovative performances, which previously we could not even dream of," said Gergiev.
"I feel certain that 25 years from now, Mariinsky II will be seen as a St Petersburg landmark in its own right, recognised for its superb acoustics, dazzling production facilities and unsurpassed level of audience comfort."
Gergiev will conduct at the opening, which will be broadcast live on television. Spanish tenor Placido Domingo, Russian opera singer Olga Borodina, and violinist and viola player Yuri Bashmet are among the performers at the lavish gala performance.
The new theatre is one of several grand projects intended to show what Russia can achieve, most notably the 2014 Sochi Winter Olympics, Putin's pet idea.
With the latest technology -- although it has a chandelier in the VIP box to make prominent guests feel at home -- the Mariinsky II is a world away from the original Mariinsky Theatre, which was sumptuously decorated in gold and red.
Built in 1860, the pastel green Mariinsky was the focus of cultural life in St Petersburg for decades.
Tchaikovsky's Nutcracker was premiered there in 1892. Eighteen years earlier, Mussorgsky first showed his opera Boris Godunov to a packed house.
But Gergiev, who turns 60 on the day of the concert, decided the old Mariinsky theatre was no longer adequate for his plans.
As the head of the ballet and opera companies that were called the Kirov Opera and Kirov Ballet in Soviet times before reverting to the Mariinsky name in 1992, Gergiev runs a huge cultural empire which needed a modern home.
The project has not been without difficulties. Costs soared when one design was killed after work had already started, and at least three firms have been involved in the construction.
Gergiev denied last year there was serious discontent in the ballet troupe over pay and conditions after dancers wrote a letter of complaint.
But the Mariinsky has largely avoided the scandals that Moscow's Bolshoi Theatre has suffered in recent years.
Not only was Sergei Filin, the artistic director of the Bolshoi Ballet, almost blinded in an acid attack in January but the Bolshoi's programme has at times faced criticism since the theatre reopened in 2011 after a six-year renovation.
Ballerina Viktoria Krasnokutskaya was one of several performers who said the new technical equipment at the Mariinsky made a huge difference, allowing scenes to be changed easily and quickly.
"Inside the theatre, the seating area is very beautiful ... It is very light and spacious," she said.
Designed by Toronto-based Diamond Schmitt Architects, the interior of the building glows in light reflected from wall panels made of Italian onyx that stretch several storeys high.
Glass and metal walkways slice through the building, which looks over a canal at the old Mariinsky through large windows. The two theatres are connected by a bridge and performances will be staged at both venues.
The two buildings could hardly be more different. The new one stands out against the late 19th-century edifices that surround it in a city landscape immortalised in the works of Gogol and Dostoyevsky.
"(Before it was built) there were fears that this would look like an apartment block or a shopping mall. People do not understand what this building is," said city resident Irene Vargo.
Builders demolished an entire block for the new theatre, razing the constructivist building of the Palace of Culture of the First Five Year Plan and the remnants of a Lithuanian market and school, built in 1930.
Alexander Margolis, head of the St Petersburg branch of the Russian Society for the Protection of Monuments of History and Culture, said they had destroyed the World Heritage Site that lies at the heart of the city.
"I think it's not just an urban planning mistake, in my opinion this is an urban crime because there was an intrusion into one of the most unique corners of St Petersburg's historical centre," he said.
Alexei Kovalev, a deputy in St Petersburg's legislative assembly, said the building was "disgusting".
"My opinion is that it should be torn down," he said. "I don't care what is inside it. Gergiev should be fired." (Reporting by Liza Dobkina; Writing by Elizabeth Piper; Editing by Timothy Heritage and Giles Elgood)