I agree with ArmyRN, try to find an ROTC scholarship to increase your chances of being selected. If you can't, you would just get your BSN and then apply for the NTP (Nurse Transition Program) for the Air Force. If you want to be an RN, not a medic, you'll want to get your degree ASAP. If you'd rather serve first you can enlist as a medic, but then you may or may not be able to get your degree as quickly, since you'll be enlisted for that first contract of 3-4 years.
For the NTP, it's very competitive currently because the military is downsizing. It may change in 3-4 years but who knows. I'm applying this summer and there are only 35 med-surg slots and 5-10 OB slots. That's for the US, not just a state. If you really want to be an RN one day with the Air Force you'll definitely need to build a strong resume over time (volunteer work, leadership opportunities, work if you can, community involvement, etc.). The NTP board looks at your resume, some short-answer questions about yourself, letters of recommendation (from professors/nurses), your GPA/transcripts, and an interview with a chief nurse. Also, they've just changed the GPA requirement. In order to apply this year for NTP all applicants must have a 3.4 GPA, so you'll want to keep that GPA up in college.
You're looking pretty far ahead, which is good if you're serious about this. There are a lot of good discussions on this site about Air Force nursing and applying. Look around if you're still curious!