THE future of opera and ballet at the Sydney Opera House is under threat because of chronic sound, mechanical and backstage problems, its top figures have warned.

"Unless something is done over the next few years, the house will become dysfunctional and ultimately obsolete," said the music director of Opera Australia, Richard Hickox. "It's not a luxury, it's a necessity that something is done."

The Herald was given unprecedented access during a month-long examination of problems at the Opera House. Conditions in the Opera Theatre's orchestra pit, the wings and backstage are so cramped and dangerous for artists and crew that programming is increasingly being revised.

Dr Norman Gillespie, chief executive of the Opera House, agrees the future of the Opera Theatre is at risk.

"There is a real danger our Opera Theatre becomes obsolete in terms of its performing repertoire," he said. "If those challenges become so great that we have to curtail any of our artistic companies, then I think you have a real problem."

The lack of wing space - about two metres wide - was a major difficulty for dancers, according to Richard Evans, executive director of the Australian Ballet. "When you see someone do a grand jete across the stage they are quite often grand jete-ing straight into the walls," he said.

Critical pieces of machinery - stage lifts and flying systems installed before the house opened in 1973 - are reaching the end of their lifespan. Technical problems last year interrupted a performance of Handel's Rinaldo, resulting in a scene having to be restarted, and a lift malfunction threatened a performance of Prokofiev's The Love for Three Oranges.

Mr Hickox feared the breakdown of the old machinery would force the cancellation of entire performances.

"The machinery is breaking down. If the stage machinery is breaking down, you can't have a show," he said. "It's had 30-odd years of doing eight shows a week, and things wear out."

His comments come as the Opera House considers radical plans by the original architect Joern Utzon to solve the shortcomings.

Opera House officials have refused to discuss the costs involved, but they are believed to be about $700 million. The plans involve lowering the stage and auditorium in the Opera Theatre and cutting a tie beam that holds the structure together.

Among the key problems in the Opera Theatre - the most prestigious of the Opera House's five venues - is the orchestra pit, where stricter health regulations for acceptable decibel levels increasingly govern what opera can be performed.

"If we do the loudest opera - and Turandot is about the loudest opera - we'll have to make sure that in the same week there will be some Handel or Mozart, which have lower decibel readings so the average over the week doesn't exceed the legal limits. That's a new ingredient to our mix," Mr Hickox said.

Opera Australia, the principal user of the Opera House, estimates it has spent $220,000 to roster extra musicians for its Sydney season this year to protect the hearing of its musicians.

The Australian Ballet faces similar costs, according to Mr Evans. The small, narrow stage limits dancers, designers and choreographers.

"It's shorter and skinnier than anywhere else. That means we have to dramatically alter some of our sets," Mr Evans said.

Its new production of The Nutcracker would require two versions of the set - one each for Sydney and Melbourne - which would add $500,000 to costs.

Dr Gillespie described conditions behind the scenes as "Dickensian". Wing space, lighting rigs and storage were all inadequate for one of the busiest opera companies in the world.

Conditions in the Opera Theatre pit were unacceptable.

"It has the dubious distinction of being the only orchestra pit where the brass are housed in a separate enclosure. That's out of necessity for some noise protection, but it is very dysfunctional," Dr Gillespie said.

Because of the theatre's unique construction, lowering the stage and auditorium were the only way to create better sightlines, additional seating, wing and storage space.

"The only way is down,"' Dr Gillespie said. This is because of the way in which the public areas, including the foyer, wrap around the theatre.

The grand plan to revive the Opera House would require the closure of the Opera Theatre for more than two years.

The theatre is already expected to close within a couple of years for essential maintenance, Dr Gillespie said.

"If you are going to have to close to do major essential upgrade, that's the time to do a complete overhaul."

Doing nothing was not an option, he said.