Mr Barr made the comments during a Legislative Assembly Estimates committee hearing on Friday, when he was asked about the progress of the proposed commission, which the government recently delayed until 2019.

While all three parties have backed the commission idea since the 2016 election campaign, some differences have emerged, particularly over proposed retrospective powers the commission could be given to investigate issues before its planned start date of January next year.

A committee that iniatially investigated the proposed recommended it be given retrospective powers, which committee chairman, Greens leader Shane Rattenbury, had said it needed so it wasn't left waiting around for a scandal to investigate.

But the government responded to the proposal by saying it was of the view the commission "should focus on prospective and current matters, with limited ability to review retrospective or previous matters".

It is understood there has been an ongoing tussle between the Greens, which want retrospectivity to form part of the proposed legislation, and the government which wants such powers to be limited, though it is unclear how.

If the commission was given no retrospective powers, it may be unable to investigate a series of recent scandals including the Dickson land swap, and a series of controversial deals executed by the former Land Development Agency.

On Friday, Mr Barr told the committee that if the commission was to have retrospective powers, he believed a defined period for such powers could date back to 1989, when the territory became self-governed.

"Certainly its my strong view that retrospectivity should apply and it should go all the way back to the commencement of self-governing in the territory, that's the only logical date that you could seek to draw a line," he said.

"I think going back prior to self-government would be absurd, but it should be able to reach back to 1989."

Mr Barr also said the new committee inquiry, which will examine an Opposition bill and an as-yet unreleased government bill, would need to consider a broader test, with thresholds for what could be investigated, not just a time limit.

Another sticking point the committee is expected to examine is whether the commission's remit should cover ACT Policing, a workforce contracted by the government from the federal police, who have been vocally opposed to being included in the scope.

While the committee recommended the territory's police force be covered, the government has committed only to progressing the issue with the Commonwealth, and though the level of vigour it is pursuing that issue is unclear.

The committee will also have to come to a decision on whether government contractors and other third parties should be included, with the government only pledging to consider the issue in drawing up its bill.

On that issue, the Opposition's bill proposes including all such third parties, including explicitly listing building certifiers as fulfilling a public service role, and the committee originally backed including such people.

Mr Barr said he hoped a consensus on the final legislation could be reached to allow the legislation to be introduced, debated and passed in the final sitting week this calendar year in late November, though he said predicting outcomes on the floor was "a fraught process".