The government has failed to identify how directly elected police and crime commissioners will improve governance, add value and engage the public better, police authority chairmen claim.
Paying for expensive elections to create the commissioners would come amid deep policing and public sector budget cuts, they wrote in a letter to David Cameron.
And they voiced doubt about how individual commissioners, who would replace police authorities under the government plans, could effectively perform their duties without significant support from staff.
In the letter, the chairmen from police authorities in Kent, Hampshire, Surrey and Thames Valley also said the proposed roles will hold fewer powers than those already available to them.
They wrote: “If the police and crime commissioner has no greater ability to direct chief police officers than the existing police authorities, how will they be more successful in delivering the outcomes that local people desire?”
The creation of elected commissioners is one of the controversial proposals in the government’s plans for policing reform, on which consultation ended last month.
Under home secretary Theresa May’s plans, each of the 43 police forces in England and Wales will be overseen by a directly elected commissioner for a maximum of two, four-year terms, beginning in May 2012.
Police have been held to account locally by police authorities since they were established as part of the major reform of policing in 1964.
But the government has said they “remain too invisible to the public” and that the public does not know how to influence the way policing is delivered in their communities.
The chairmen of the South-East police authorities said in their letter that commissioners’ ability to hold forces to account will be “unachievable” when there is only a “two-way dialogue”.
A Home Office spokesman said: “Police authorities don’t work - only 7% of the public has ever even heard of them.
“We are determined to hand back power to the people and will work hard to ensure a new more democratically accountable system costs no more than police authorities do now.
“Getting police back on the beat and helping to cut crime means turning away from bureaucracy and returning to common sense policing.”