Even as a misdemeanor, this will be something that you will have to disclose in the hiring process. This will not automatically bar you from employment, but it will certainly be a hurdle for you to clear.
You will be given opportunity in interviews to explain the situation, and the department will have to determine whether or not the feel you are a liability.
Competition for law enforcement jobs is pretty tough with most agencies. The further this incident fades into your past the less significant it will be. So long as you do not add to it with drug use, collections, etc then you should be able to find an agency willing to take you on.
Do yourself a favor and be honest and upfront about it. If you try to minimize it or obscure it in any way, do not expect to get hired. Also, when it comes time to fill out the paperwork regarding prior convictions, be sure to ASK about your situation to make sure you put it down on paper right. You will likely be told to mark that you have the felony, and will have opportunity to explain how it was later reduced. If you mark that it was a misdemeanor and the investigator later sees that it was originally a felony, it could create a problem.