Four Midland constabularies may merge to create England and Wales' second biggest police force, new plans show.
Some police authorities are worried by the cost of mergers
The West Midlands, Staffordshire, and Warwickshire forces support a merger but West Mercia objects saying a new force would be "too big".
It is part of a national plan to create as few as 12 larger police forces from the current 43.
At a news conference on Thursday the Chief Constable of Warwickshire said the merger was the way forward.
John Burbeck said: "There are still some issues to be resolved - the question of how to fund the new force, the question of accountability.
"We're very conscious of the fact that not only does the force need to be held accountable, but... it's important that local people, locally elected representatives, can influence local policing."
Home Secretary Charles Clarke has been criticised over plans to merge the current police forces.
But he insists mergers will help police combat terrorism and organised crime.
The Home Office has set a deadline of Friday for all forces' proposals for the changes.
Paul Tonks, chairman of the West Midlands Police Federation, said the changes would make sense at a time when crime knew "no boundaries."
"I can see the benefits from a policing perspective of the three or even potentially the four forces coming together to fight the drugs crime, the gun crime, the major investigations, the murder investigations ... You know crime now has no boundaries," he said.
"Criminals do travel far easier and areas are far more accessible now than ever."
A merged West Midlands force would have 14,000 officers, and 7,000 staff, second in numbers only to the Metropolitan Police.
But West Mercia - recently ranked as the top-performing police force - will tell Mr Clarke that it wants to go it alone.
Paul Deenan, chairman of the West Mercia Police Authority, said moving to a "massive model" was "untested at the moment".
"We can talk about efficiency savings but they could be several years down the road," he told BBC Radio 4's Today programme.
The uncertainty of the changes would lead to "morale issues", he warned.
Opposition and Labour MPs have also criticised the pace of the changes and what they see as a loss of localised policing.
But Staffordshire Police Authority chairman Mike Poulter, whose force is in favour of the West Midlands merger, said a bigger force would "enhance neighbourhood policing".
But the proposed new force could not work without West Mercia, and the home secretary "must resolve that issue", he said.
A report by Her Majesty's Inspectorate of Constabulary (HMIC) said forces with fewer than 4,000 officers were not equipped to fight sophisticated modern crime.
Although a number of other forces in England and Wales are thought to be willing to merge, some want reassurances that they will not have to fund the costs of restructuring.
Advocates of the changes say the plans could save up to £2.3bn over 10 years. Ministers have told force leaders to borrow money to meet the merger costs.