If your goal is career LE then I would say enlist first. The military experience will give you service points on the law enforcement exam, no matter what job you have in the military. You can earn credits in the service, and most departments I know of will have the requirement of either college OR priort service. So if you come out of the Marines (most of the guys at local PD are former Marines, a few AF and one army) then apply you can still get hired, you have the service points AND you have credit hours you can then apply towards a fresh degree.