Fewer than a third of the 43 forces in England and Wales back government plans for mergers, the Association of Police Authorities (APA) has said.
The Home Office says merging forces will modernise policing
The home secretary says merging the police into as few as 12 forces will make them more efficient and better at fighting terrorism and organised crime.
He set a Friday deadline for every force to have responded to the plans.
But the APA said the proposals were inadequate and that only 13 forces had expressed a desire to merge.
The plans to merge police forces were announced by Home Secretary Charles Clarke after 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.
The Home Office is expecting forces to submit detailed business plans on how they intend to proceed.
However, a spokesman said no figures on the number which did so would be released on Friday.
Association of Chief Police Officers president Chris Fox said the plans offered forces a "great opportunity".
He told BBC Radio 4's Today programme: "We are currently organised in a way that was designed to deal with Britain in the 1960s and Britain in the 21st century is slightly different.
"We've got to safeguard local policing but deal with the new world - very complicated, strategic crime, organised crime," he said.
APA chairman Bob Jones said they shared with Mr Clarke the need to "raise our game" in terms of counter-terrorism, serious organised crime, major murder investigations.
"However, we have been given very little time to actually bring those plans together and we are also lacking in information, particularly about the financing and support for those particular plans, which means we don't feel that those plans are adequate and can guarantee improved performance in the near future," he said.
The plans have also been criticised by Conservative and Liberal Democrat MPs, with both parties saying they are being pushed through too quickly and with too little consultation.
Lib Dem home affairs spokesman Mark Oaten also accused the government of setting an "unrealistic target for police mergers".
As a result it was "no surprise" police had been unable to reach the deadline, he added.
And former Tory leader Michael Howard, who was home secretary at the time of an earlier report which proposed merging forces, said it was a "most humiliating snub" to Mr Clarke that "not a single one of the 43 police authorities" had submitted the detailed business plan by the deadline.
He said he did not rule mergers as a way forward, but said there were different ways for authorities to co-operate, including federation and some also felt they could deal better with challenges as "stand alone" authorities.
The Home Office says the government knows the deadline is "challenging" but that there will be further discussions involving all police forces and authorities in January to resolve any outstanding issues.