Police bobbies are now spending as little as half their time on the beat, a watchdog has revealed.
Frontline officers are increasingly "tucked away" after being diverted on to tasks such as guarding crime scenes, processing prisoners and staffing front counters rather than pounding the streets.
In one area a reduction in the neighbourhood police presence was followed by a surge in reports of anti-social behaviour.
Meanwhile, in some forces there was evidence that PCSOs, who do not have full police powers, were responsible for investigations of low-level crime such as shoplifting, HM Inspectorate of Constabulary (HMIC) said.
Inspections of forces in England and Wales suggested neighbourhood officers, whose principal function is prevention work and community engagement, are more frequently being removed for short periods from their regular duties to carry out other functions.
Some officers estimated that only about 50% of their time is spent in neighbourhoods on preventative duties, HM Inspector of Constabulary Zoe Billingham said.
"For the rest of the time they are tucked away, not visible - doing worthy stuff no doubt - but not visible, not doing their core role," she added.
Ms Billingham said forces' good performance in preventing crime could be at risk.
She said: "Neighbourhood teams have the best knowledge of victims and offenders on their patch. They are the vital eyes and ears to gather intelligence for a whole range of criminality up to the most serious, including terrorism.
"I think there is a risk that the police service is sleepwalking to a return to their old model of policing where police are isolated from communities.
"That's why we are sounding this alarm bell now. Neighbourhood policing is a cornerstone of the British policing model and we can't afford to lose it."
Essex Police was cited by HMIC after indications of a spike in reports of anti-social behaviour following a reduction in its neighbourhood presence last summer.
The force said: "During last summer some officers were temporarily redeployed from their roles to help investigation and safeguarding work on high-priority outstanding incidents including domestic abuse and missing children cases.
"While anecdotally there were reports of more anti-social behaviour incidents during this time, across the year there were nearly 3,000 fewer incidents than in 2014, a 6.6% decrease.
"The HMIC report makes clear that Essex has fewer ASB incidents per head than the England and Wales force average."
In the last parliament, police faced spending squeezes and officer numbers fell by almost 17,000. However, Ms Billingham said it was not "inevitable" that neighbourhood presences should be eroded.
Shadow policing minister Jack Dromey said: "The police are now spread so thinly that they are struggling to act as 'eyes and ears' on our streets - undermining, just when national security is at risk, efforts to counter the threat we face from terrorism.
"It is the worst possible time to slash bobbies on the beat."
Chancellor George Osborne has ruled out fresh cuts.
Policing minister Mike Penning said chief constables and police and crime commissioners "have no excuse whatsoever not to deliver at least good quality policing".
He added: "Since 2010, this Government has reformed policing to make it more professional, less bureaucratic for officers and more responsive to victims, and last year we protected police budgets for the next four years, once local precept is taken into account."
National Police Chiefs' Council lead for crime operations Jon Murphy said: "Neighbourhood policing is vital in preventing crime, anti-social behaviour and terrorism.
"Police chiefs have protected it when responding to previous budget cuts and are now considering the best way to deliver effective preventative policing in their communities while managing increasing demand in investigating complex, resource intensive crimes."
HMIC identified "endemic" delays of up to a year in extracting and analysing evidence from mobile phones and computers as another major concern.
Each of the 43 forces was rated on overall effectiveness in reducing crime and keeping people safe. More than a third - 18 - "require improvement", 24 are "good" and one is "outstanding".
Almost all forces are good at preventing crime and anti-social behaviour and there were "big improvements" in the response to domestic abuse victims.