The deal, signed with Carbon Motors Corporation, includes the delivery of "more than 240,000" six-cylinder engines, transmissions and exhaust systems, a statement said.
It estimated the contract's value in the "billions of euros" over a time frame that was not specified.
The German powertrains would help US police forces reduce fuel consumption and carbon emissions by 40 percent, BMW sales director Ian Robertson was quoted as saying.
Carbon Motors was founded in 2003 by a former Ford executive to produce one model, the E7, which it plans to sell as a police crusier.
No roll-out date has been set so far for the vehicle, which is also to feature advanced video surveillance equipment, warning lights and ballistic protection.