Norfolk's Chief Constable Simon Bailey said police must focus on "contact abusers" - people who commit abuse - an estimated 16-50% of those who view it.
Mr Bailey, the Association of Chief Police Officers' lead for child protection, said police "simply cannot cope" with the numbers viewing images.
But a former social work leader said those watching abuse were "causing" it.
Mr Bailey said he understood how controversial his proposal was, and that most people would want those who viewed child abuse locked up.
He told BBC Radio 4's The World Tonight that viewing abuse was an "abhorrent crime" but there was a limit to "what policing can do" due to the sheer numbers of people doing it.
"Law enforcement has to come up with a model for dealing with the people that pose the greatest threat to children in the form of contact abuse whilst dealing with those people that don't pose the threat in a different way," he said.
He said police had commissioned a review of all available academic research, and the results suggested between 16% and 50% of people who viewed indecent images of children "were then likely to be contact abusers".
Mr Bailey said 90% of child abuse took place within the home and believed most people would say those who view child abuse must have a "mental health issue".
"We should be actively working with clinicians who can get to the bottom of that perverse attraction and starting to help those people who would seek to derive some pleasure from looking at a child being abused," he said.
David Niven, former chairman of the British Association of Social Workers, said the idea that people who viewed abuse were no threat to children was "ridiculous".
He said "consumers" of abuse images created a market for it, and were therefore "causing the abuse".
Mr Niven agreed there should be more treatment but said there was "no such thing as a cure".
He said other addicts only harmed themselves - but "in this case other victims are children".
"So you've got to have dual controls, you've got to have the threat of enforcement as well as the provision of treatment," he said.
People who view child sex abuse online should get medical help - not prison time - a senior police officer says.