Society president Sarah Avery has urged a public interest test, such as the one that applies in Victoria, to decide whether hearings are private or public.

In Victoria, hearings are private unless there are "exceptional circumstances" and a public hearing is in the public interest because the corruption is systemic or especially serious. Public hearings are only held if they can be held without causing unreasonable damage to someone's reputation.

Ms Avery said the ACT could devise its own public interest test, but the promised commission must be able to balance "public interest in disclosing and exposing corrupt behaviour with the potential disproportionate damage to reputation".

She made her comments in a submission to a parliamentary inquiry that is working out the detail of an ACT corruption watchdog.

Private or public hearings are one of the key decisions facing the government. Another is to what extent it will be able to investigate allegations against police officers.

And it is now facing a suggestion that the ACT could avoid setting up its own corruption body altogether, and instead piggyback off a federal corruption body.

The suggestion was made by ACT Ombudsman Michael Manthorpe under the heading "an alternative", in his submission to the inquiry. He said given the Senate is now looking at a federal corruption body, with its report due in August, it was open to the ACT to "explore an arrangement ... for the provision of relevant services to the ACT".

The public sector union is urging no public hearings except in extraordinary circumstances, saying the risk of people's reputations being damaged is worse in a small jurisdiction such as the ACT.

The parliament's independent ethics adviser, Stephen Skehill, also suggests hearings should be private, with public hearings risking "unwarranted damage to the reputation and livelihood of potentially innocent persons", and discouraging people from coming forward. Investigations should remain "behind closed doors" until charges were laid, he said.

But the Australia Institute said regular public hearings, like those in NSW, were critical. The NSW commission was far more effective than other state bodies, having held 28 public hearings over four years. It had made corrupt conduct findings against 123 people, referring 76 people to the director of public prosecutions.

In contrast, the Queensland commission had held no public hearings, made no corrupt conduct findings and referred 32 people; and the Victorian commission had held four public hearings, made no corruption findings and referred six people.

The Griffith Narrabundah Community Association also argues strongly for public hearings, comparing it to criminal cases which it says are heard in public for good reason.

"On what basis is taxpayers' money to be spent on investigations only to have those suspected of wrongdoing cross examined in private?" president John Edquist asked, insisting justice must not only be done, but be seen to be done.

But Ms Avery, for the Law Society, said as a general rule hearings should be in private, with the power to hold public hearings in specified circumstances.

The society supported the establishment of a commission, but it was "vital" the right balance was struck between effective operation and properly protecting people who were investigated.

The commission should cover all public sector agencies, public officials and politicians, Ms Avery said. And it should go beyond criminal allegations to cover "a broader range of undesirable conduct, including matters where there exists a reasonable suspicion of corruption, conflicts of interest and/or undue influence".

The rules should be carefully written to prevent government functions being placed beyond the reach of the commission because they were contracted out, but covering all government contractors would be too broad, she said.

Protocols should be set up to avoid duplication with the Judicial Council, which investigates police, the Auditor-General and others, she said.

The Law Society supports coercive powers for the commission, but it said there should be proper controls. The commission should not be able to issue search warrants in its own right, but should have to apply to the courts for warrants for surveillance, entry, search and seizure.

The parliamentary inquiry into the new corruption body holds its first public hearing on Thursday, July 20. Details.