West Midlands Police proposes a total of 2,764 job cuts
More than 2,700 jobs are to be cut at West Midlands Police by 2015 - 450 more than expected.
A report by HM Inspectorate of Constabulary (HMIC) previously estimated 2,314 jobs would go.
But a meeting held by the West Midlands Police Authority has put the figure at 2,764. West Midlands Police needs to save £126m in the next four years.
Chair of West Midlands Police Federation Andy Gilbert said: "There will be less of a public service."
He said: "We understand there have to be cuts - it's the scale and the depth of the cuts that are the concern.
"We thought 12% would not impact on the front line but cuts of almost 20% will do, we're going to have to work differently.
"Taking that amount of resources away [will] have a detrimental effect."
The policy authority said there would be an overall reduction of 2,764 people split between 1,165 police officers, 1,477 police staff and 122 police community support officers (PCSOs).
A spokeswoman from West Midlands Police Authority said the original figure given by the force in September 2010 was during "very early planning".
She said: "It was an estimate and was always subject to revision.
"Staff numbers are difficult to estimate in long-term circumstances."