Deputy Chief Constable Rose Fitzpatrick, who will be head of territorial policing, admitted the situation was “not ideal”.
The public sector union Unison believes backfilling – police officers doing back-office jobs – is already taking place and will increase under a single force.
Ms Fitzpatrick also revealed that police would consider reducing control rooms, raising the possibility that an emergency call from Inverness, for example, could be answered in Glasgow or Edinburgh.
An estimated 1,400 jobs are to be cut by Police Scotland, according to reports.
Ms Fitzpatrick said police would look at different ways of working to reduce the need for officers to carry out civilian roles. “We don’t want to use officers in roles which don’t use their police officer skills,” she said. “But it would be foolish to say, in the short term, we would not use them to fill those gaps.
“It’s not an ideal situation and isn’t one we would want to have to use in the long term.”
She denied the job cuts made it more likely that police would be asked to backfill. “We have to continue to provide a service to the public,” Ms Fitzpatrick said.
Police in Scotland start on salaries of more than £23,000. Unison believes in some cases they will be standing in for staff who are on half their salary.
The Scottish Government has successfully raised police numbers by more than 1,000 since 2007, and insists this should not be jeopardised by the move to a single force, with a savings target of £1.7 billion over 15 years.
However, Chief Constable Stephen House has admitted the current total may not be sustainable beyond next year.
Dave Watson, Unison’s head of bargaining and campaigns, said police were “handcuffed” by the Scottish Government.
“Senior police officers are not in control of the workforce structure,” he said. “This is being determined by [justice secretary] Kenny MacAskill. He has put handcuffs on them.”
He added: “We are absolutely going to see more backfilling. There is no alternative if we stick to the 17,234 officers and make the scale of savings that the new force is expected to make.” A Scottish Government spokeswoman denied that backfilling was routine.
She added: “The deployment of officers is a matter for the Police Service of Scotland, who will ensure their skills – and powers – are used in the most effective and efficient way in terms of tackling crime and the public purse.”