Justice Secretary Kenny MacAskill has warned Scotland's eight police forces of "unprecedented challenges" ahead.
He said the Scottish government is giving the police £1.4bn this year but, with cuts in public spending, changes are needed.
The minister said police funding was £235m a year more than under the previous Labour-Liberal Democrat Executive.
And Mr MacAskill urged forces to work together more to avoid duplication.
He was speaking at an Association of Chief Police Officers Scotland (Acpos) conference in Cumbernauld.
Mr MacAskill said: "It will not be sustainable to carry on as before. We are a small country and we can no longer afford to do everything eight times over.
"This means 'fresh thinking and new approaches'."
He added: "We are entering a period where we will face major economic and financial challenges for several years to come."
The Scottish government's chief economic adviser has said public services may be cut by as much as £35bn over the next 15 years.
Mr MacAskill said: "We need to be planning now for a new financial climate that lasts for perhaps a generation - there can be no doubt that we are entering a phase of unprecedented challenges.
"Whether it is procurement, IT, or back-office functions, we need to focus on cutting duplication and finding more efficient ways to work."
A Scottish government spokeswoman stressed later that ministers were committed to keeping eight police forces.
Mr MacAskill also told the conference: "I do not have a blueprint for how Scottish policing will look in five years' time, or 15 years' time.
"But looking at the figures, we know that it will not be sustainable to carry on as before."
Labour justice spokesman Richard Baker said: "Kenny MacAskill calls for fresh thinking and new approaches but it's obvious that he's done none of that himself."
Mr Baker said that 1,000 support staff have been removed, "thanks to SNP cuts".
He added that Scottish government plans to extend community service while bringing in a presumption against short-term jail sentences would cost millions.
Liberal Democrat justice spokesman Robert Brown said: "Mr MacAskill's comments cast serious doubt on their stated commitment both to retaining eight police forces in Scotland and to achieving and keeping 1,000 extra police officers".