Whats the best move in starting off law enforcement?

my primary aspirations is to b a cop, and my main questions conscern college courses and departments to start off in, im thinkin the best college course would be puplic administration and criminal justice, and im thinkin of starting off in a big department like LAPD since i could more easily secure a position in either narcotics or like work in a K9 unit or something, so id get my credentials is a specific field there, then move to a smaller department so i have more of a chance to secure a specific job there with the credentials i alredy have, since i hear there r fewer oopenings with smaller departments. thoughts? suggestions? id appreciate it, especially from vet officers