Labour wants to merge them into one single force, and the SNP also wants a reduction.
Mr Graham said he has had talks with the single force's chief constable, Stephen House.
BBC: Local policing 'will continue' in new single Scots force
Mr Graham said Northern Constabulary had started preparations for the transition to a single force.
BBC: Local policing 'will continue' in new single Scots force
It was the last meritorious awards ceremony before the launch of the single force Police Scotland in April.
The idea of a single force was outlined in a government consultation on the future of the police service.
If a single force was not possible, he added there were "a number of different things that could be done".
Labour's Iain Gray said a single force would protect jobs, but Lib Dem Tavish Scott said it may harm police autonomy.
Issues surrounding who should have day-to-day control of human resources and finance functions in the new single force have yet to be fully settled.
Grampian Police chief constable Colin McKerracher told BBC Scotland he was in favour of some kind of restructuring, but feared a single force could mean funding issues.
In a move that American defence planners might envy, the army, air force and navy will be linked into a single force geared to rapid, long-range deployment.
Central Scotland Police announced in October that, because of the single force, it had disbanded its pipe and drum band and reformed it as a civilian one, the Bannockburn and District Pipe Band.
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But one of Mr Allen's local authority partners, Eric Milligan, who sits on the Lothian and Borders Police Board, said the idea of a single force betrayed the localised history of Scottish policing and threatened the independence of the force.
The consultation, to get under way next month, will outline three options for fire and police services - eight services with enhanced collaboration between them, a regional structure with fewer boards, or a single service for fire and a single force for police.
Labour and the Conservatives both support a single police force but the Liberal Democrats remain opposed.
The changes have been made ahead of the launch of the new single police force.
BBC: Highland and island stations closed to public overnight
Because every single police force in the country is gradually phasing out traffic division.
An 11th-hour intervention has ended a stand-off overshadowing the creation of Scotland's new single police force.
BBC: Deal struck to end impasse over police force's functions
Scotland's eight police forces are being merged into a single Scottish force from the start of April.
Single police force boss Stephen House and police authority head Vic Emery are yet to agree a way forward.
Improve the way the problem is identified by Scotland's new single police force.
Now the new single police force for Scotland, which begins operations on 1 April, will adopt the idea nationwide.
The Tories' John Lamont backed a single police force but said locally elected police commissioners were needed to improve accountability.
Suggestions for a single county force have been echoed by at least one county MP, who thinks that Cornwall could benefit.
Party leader Annabel Goldie told the event in Aviemore that she supported reducing Scotland's eight police forces to a single national force.
Willie Rennie, of the Liberal Democrats, fared rather better with a "why oh why" lament about plans for a single police force.
Cosla said the Scottish government had already made up its mind that a single police force and fire service was the way forward.
Holyrood's justice committee has issued an ultimatum to the new single police force and the Scottish Police Authority to resolve a so-called power struggle.
Scottish Liberal Democrat justice spokeswoman Alison McInnes said she remained concerned about the impact a single police force could have upon local policing in Scotland.
Miss Goldie, who like Mr Gray will leave her leader post later in the year, said there were measures her party could support including a single police force.
BBC: Scots ministers to reform police, jobs and alcohol laws
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