Some 25,000 police officers could be axed amid plans to merge the 42 police forces in England and Wales, the leader of the Police Federation has warned.
Jan Berry warned police officers could be replaced by civilian patrols
Jan Berry told the federation's annual conference the aim could be to pay for 25,000 community support officers promised by the government by 2008.
Replacing police with civilian patrols would be a "tragedy", she said.
But Home Secretary John Reid said CSOs should not be used in place of police and there were no plans to do so.
Addressing the conference, Ms Berry said Association of Chief Police Officers (Acpo) was planning to announce the proposals at its annual conference next week.
She said police numbers had already fallen from 142,000 last year to 141,000.
She said: "Acpo say they can lose 25,000 police officers over the next five years. That would bring us down to 116,000.
"If we continue down-sizing them, you will probably end up with a paramilitary force who only deal with confrontational situations.
"That would be a terrible tragedy for British policing."
She said it was difficult to say whether the plan to cut 25,000 officers was designed to pay for the 25,000 promised CSOs.
But she pointed out the Home Office had not guaranteed to pay for the new civilian patrols beyond 2008, leaving forces with the prospect of coming up with extra millions to pay for them.
She added: "If there is a disaster and we don't have the resources to deal with it, we are going to get the blame and that's totally unfair."
Cuts 'not true'
Acpo chief Ken Jones said it had no plans to reduce police numbers by 25,000, saying: "Moreover, Acpo would not stand by and oversee such a cut in numbers.
"However, it would be irresponsible of us not to look at future scenarios, even those we do not like.
"The fact is that if all signalled reforms were to take place, including restructuring, this would inevitably impact on the money we have to pay for police officers and police staff.
"We are actively working with government to avoid this situation and they have agreed that the police reform programme must be reprioritised so as to make it sensible and affordable."
Mr Reid confirmed Acpo had been looking at a range of possible options including "a worst case scenario".
But he said it was not planning to substitute CSOs for police officers.
He said: "It is not my view that we ought to be using CSOs to substitute for police," he added.
Shadow home secretary David Davis said that if the 25,000 cut in officers went ahead it would be "a direct result of successive Labour home secretaries playing fast and loose with the funding of our police service".
Earlier, the home secretary gave a speech to the conference in which he indicated he would look again at how the force mergers were being handled.
Mr Reid said the present way forces were organised did not meet today's demands and he agreed with the "destination" outlined in existing policy.
But he was not sure about the rate of change or whether people were "in the right buses".
He also promised adjustments to controversial human rights legislation to make sure the rights of the few did not come before public safety.
And he said there was a need to address the public perception that the justice system was unfair and gave more consideration to the rights of criminals than to those of the "hard-working citizen".