"But it's not working, it's not appropriate, it's not our policy ... It would take something seismic to convince me that three strikes should be retained. It'd go."
The policy has been criticised as removing judges' discretion, leading to sentences disproportionate to the crime.
But Corrections Minister Judith Collins said three strikes was an effective deterrent and should not be repealed. "Why would you do that? You're talking about the high-end violent recidivist offenders, exactly the people you want locked up."
She said deterrence had contributed to the predicted fall in the prison muster, even though the Ministry of Justice report did not credit three strikes as a factor.
"It does work, because of the comments that police and Corrections are getting from prisoners," Ms Collins said.
Labour is also promising 145 extra constables, including changing the 62 one-person police stations in small communities around the country into two-people stations.
Mr Cosgrove said that when the rural stations needed back-up it sometimes took an hour to arrive from the city.
The policy also focuses on low-level crime and low-level criminals, on the basis that "nipping this stuff in the bud" earlier would help to prevent offenders from getting involved in more serious crimes.
Rehabilitation programmes in prison should be more open to the 80 per cent of prisoners serving less than a two-year sentence, Mr Cosgrove said.
"It will not be the length of the sentence that will be the determining factor in what programme you get, but whether the programme will aid in rehabilitation."
But Ms Collins said that already happened.
"He's so far out of date. He hasn't kept up with the number of people accessing drug and alcohol treatment programmes in our prisons, which now focus on short-term prisoners," she said.
"Clayton doesn't know what he's talking about. The fact he hasn't asked me a question about Corrections in the House since June 2010 shows it's not a high priority for Labour."
LABOUR ON CRIME
* 145 extra constables, including 62 in small communities to turn one-person stations into two-people stations, costing $96 million over four years.
* Different role for non-sworn police to help solve petty crime.
* Stronger focus on rehabilitation for prisoners on short sentences.
* Likely to repeal three-strikes law for repeat offenders.