Glen outlined one, which is the ed delay route. The rub with that is that law school is then on your dime. That may or may not be feasible for you. The other route, and the one I'd personally recommend given that your are currently in ROTC and in the future MAY have an interest in becoming a lawyer and serving in the JAG Corps, would be to commission as normal and do your line officer service. Then, after the 3-4 year mark, you will have the opportunity to apply for what's called the Funded Legal Education Program ("FLEP"). If accepted, you stay on active duty as an O-3 and the Army sends you to law school at Army expense on top of that. For those 3 years of law school you'll owe the Army 6 more years of active duty in the JAG Corps.
The rub with FLEP is that by the time you will have finished your law school commitment, you'll likely be around 13 years on active duty, and at that point it becomes hard -- I think -- to justify getting out; so in practical terms you might think of it, more or less, in terms of whether you are prepared to be a career officer. If so, then FLEP is definitely the way to try to go.
Finally, the other advantage to waiting on law school rather than immediately going for an ed delay is that, IMO, 3-4 years on active duty as a line officer will help you substantially in law school. You will be a much better law student than you likely would be coming straight from college.