Of the 88 sites in limbo, 42 have been on the list since 1999 or earlier.

A further 20 sites on the list were lodged between 2000 and 2010, figures released in answers to questions on notice revealed.

Sites on the list yet to be assessed include the Manuka and Kingston shops.

While the government said it had worked hard in recent years to whittle the list down, opposition spokeswoman for heritage Nicole Lawder said the ACT Heritage Council needed more support to get through the historical backlog.

"Clearly, the build-up of nominations comes down to a resourcing issue. Over the past two decades, the government has failed to adequately support staff who have been working hard to support the Heritage Council during the heritage nomination process.

"The new funding provided to the ACT Heritage Council has been dedicated to process development applications only. The new funding will not be spent on the nominations...meaning the backlog of heritage nominations waiting to be assessed will continue to grow.

"If these nominations didn't qualify for heritage listing 20 years ago, they probably will by the time it takes this old and tired government to look at their applications.

"To put it in perspective, Labor has been in government nearly two decades - the same amount of time it has taken the Labor government to process some of these applications."

President of Canberra & District Historical Society Nick Swain said the backlog was bad news both to those wanting to preserve the sites and those hoping to develop them.

"As long as something's been nominated it's got the same protection under the law as if the nomination has actually been accepted," he said.

"What it doesn't do is resolve the actual application.

"If someone was hoping it wouldn't be successful then they're stuck waiting."

He said it was placing the future of sites like Kingston shops - which is waiting to be assessed - in limbo.

"I think it comes down to resources basically, it certainly sounds like it needs a bit of a blitz," Mr Swain said.

"It implies the government has put a very low priority on heritage."

An Environment, Planning and Sustainable Development Directorate spokesman said many of the nominations were made before 2004 when applications required far less information.

"This means research and assessment of older nominations is more resource intensive," he said.

"It is best practice to prioritise the assessment of nominations based on priorities including development threat and applications that require an urgent decision.

"Older nominations still receive statutory recognition under the Heritage Act 2004, which requires the ACT Heritage Council to provide advice on development impacts to nominated, as well as registered places and objects."

He said the ACT government had funded an additional staff member in the heritage unit to address the backlog.

"The Council has made significant progress towards working through outstanding nominations," the spokesman said.

"At the beginning of 2008, there were 320 nominations. 232 decisions have subsequently been made, resulting in a nominations list of 88 places and objects."