Cumbria Police will have 100 fewer officers by the end of 2011 after the force confirmed budget cuts of £18.6m over the next four years.
Chief constable Craig Mackey said the "shape and structure" of the force would have to change to meet the 20% cut in government funding.
Mr Mackey pledged the reduction in officer numbers would be achieved by natural wastage.
A further 235 staff posts are also predicted to go by March 2012.
Mr Mackey said: "This is a challenging settlement for Cumbria. The constabulary will have to operate with a substantially reduced budget over the next four years.
"The total number of police officers will fall to 1,150 by September 2011. This will be a reduction of 100 officers from our position in 2009/10.
"The overall reduction in the number of officers will be achieved through natural wastage.
"The police staff establishment will drop to 600 by March 2012 - a reduction of 235 posts.
"These are without doubt challenging times, but we are firmly committed to providing the communities of Cumbria with an affordable and realistic policing service."