Three of the four Welsh chief constables have backed the idea of a single force for Wales.
It is likely that the four Welsh forces will merge into one
On Tuesday, the police chiefs were giving evidence to a parliamentary inquiry into the plans to cut the number of forces.
The UK Government says a single force for Wales is the only realistic option.
The dissenting voice, Richard Brunstrom from North Wales Police, has yet to make a decision. "My colours are still nailed to the fence," he said.
MPs on the Welsh Affairs select committee questioned the four chief constables and their police authorities on Tuesday about the planned changes.
The chief constable of Dyfed-Powys Police, Terry Grange, said if he had to restructure policing in Wales a single force would be the best option.
"I would ask myself why there are four police forces in Wales and... one would probably be the best in all honesty," he said.
Home Secretary Charles Clarke will decide on the proposals
The chief constable of North Wales Police, Richard Brunstrom, agreed that there was "a very great deal of logic" to a single force but he questioned the flexibility of the proposals.
"My concern is around whether there is enough room for manouevre, room for negotiation, room the consultation, to give legitimate expression to local identity and local accountability," he said.
There has been criticism of the short timetable Home Secretary Charles Clarke has given to examine the options.
Mr Clarke has said all forces must reorganise to meet new threats.
Those threats include organised crime and international terrorism and police forces across England and Wales have to submit their preferred options for reorganisation to the UK government by 23 December.
One of the options being considered in Wales is to merge the four forces - South Wales, Dyfed-Powys, Gwent and North Wales - into one larger all-Wales unit.
It follows a submission by of three possible restructuring options to the Home Office.
They were: to keep the existing four forces (with North Wales Police having greater partnership with Cheshire Police); merging the existing forces into two; or merging all four forces into one.
But Mr Clarke has indicated that only a single force in Wales would get his backing, and that "other stand-alone and merger options were assessed as unsuitable".
He said that in Wales one force instead of four was the only "suitable" option, which supporters argue is needed to tackle terrorism, drug trafficking and organised crime.
But the police reorganisation has been hugely controversial in Wales.
Politicians from all parties have criticised the short timetable allowed to examine the options.
On Tuesday, Welsh Assembly Members will also debate the proposed changes, before their views are referred to the Home Secretary, who will make the final decision.
There has been opposition to the plans from police authorities in Wales, with North Wales Police Authority chairman Ian Roberts accusing Mr Clarke of "acting like a bully".
Unions have also been critical and fear a possible loss of 1,000 jobs if the merger goes ahead with services being affected.