The warning came after Police and Crime Commissioner (PCC) Sir Clive Loader earlier proposed to cut £19m from the force's spending over four years.
He could not yet confirm how many jobs would go but said 'several' officer posts would be affected.
Leicestershire's Police Federation said it feared up to 300 officers could go.
If the budget proposals are approved, the cuts will take place in three phases before April 2017.
Sir Clive, who was elected as PCC in November, said: "We are already pretty lean but we are going to be leaner, smaller, less burdened by bureaucracy by making use of emerging IT, making the most of our people by making them more skilled and a greater number of our police officers doing what we want them to do."
He said he hoped the reductions would mostly occur by "natural attrition", through officers retiring or moving to other parts of the force.
He added: "We have been consulting on this since April. One of the important aspects to this plan is partner working so we have been listening to them and putting the ingredients of a cake together for six months."
John Hughes from Leicestershire Police Federation said he understood Sir Clive's difficult position but was concerned up to 300 jobs could go.
He added: "We appreciate the PCC is in a very tough position. He is hand tied by the amount of funding the government hand over.
"We can't perform as well as we have if we continue to cut.
"Officers are concerned they are working ever longer, harder and ever more isolated. It is increasingly difficult."
Chris Hanrahan from the union, UNISON, which represents police staff, said cuts to frontline policing would see civilian jobs changing and remodelled to deal with the impact.
People in Leicestershire and Rutland have nine days to comment on Sir Clive's police and crime plan.
Following that period, the plan will be presented to the Police and Crime Panel - which oversees the work of the police commissioner - for consideration at its meeting on 2 October.
Hundreds of police officers in Leicestershire could lose their jobs in the latest round of cuts, the Police Federation has said.