A spokeswoman for the Attorney-General Mark Dreyfus said the new central office of the spy agency would open midyear.

No further details were available for the project, which is costing almost two thirds of a billion dollars.

It is expected staff will move in over coming months, with the official opening being held in winter.

The building will house the 2000 employees of the country's largest and most powerful intelligence agency, the Australian Security Intelligence Organisation, responsible for national security.

The building was announced in 2007 by the Howard government, to cost $460 million.

The cost has increased several times since then - to $527 million in 2008, $589 million in 2010 and to $631 million in May last year.

The latest estimate represents a 37 per cent, $171 million, increase on the initial cost.

The Finance Department said last year the latest rise came from contractors underestimating the extent and cost of the work on ''this highly complex project''.

At the time, the December 2012 date set for ASIO staff to begin moving in had been pushed back by three months to early this year.

It has now been pushed back by another three months.

Last week another local building firm, Tread Lightly Earthmoving, became another casualty of the dispute over the ASIO building project.

The Queanbeyan company called in administrators but will continue to trade.

Tread Lightly was one of the key creditors of Urban Contractors, which went into administration in October, a move largely blamed on its involvement with the ASIO project.

The ACT government is owed nearly $400,000 for the dumping of asbestos-contaminated soil from the site.