I am currently active duty. Can I switch to Reserve if I still have an ADSO?

Yes and in fact it is encouraged. All reserve components need company grade officers, particularly those with active duty experience. But I want to prepare you, there will be a "cultural sock" and you will be encouraged to adapt when you make the switch. No big deal, you might also want to look into the AGR Program as well.

Chapter 4
Waivers and Exceptions
4–1. Requests for waiver of active duty service obligations
a. Statutory service obligations will not be waived except for the convenience of the Government or personal hardship reasons. The authority provided by this regulation to grant waivers or exceptions to this regulation will be referenced in all contractual obligations, and when not expressly incorporated, will be implied to be present.
b. Requests for waiver of non-statutory active duty service obligations, and to the method and time of fulfillment incurred under this, and other Army regulations, will be forwarded through command channels to—Commander, USA H R C ( A H R C – O P D – A ) , 2 0 0 S t o v a l l S t r e e t , A le x a n d r ia , V ir g in ia 2 2 3 3 2 – 0 4 0 0 , f o r A r my C o mp e titiv e C a t e g o r y , AMEDD officers, and OPMD managed warrant officers. Chaplains will forward requests to HQDA (DACH–PER)
3 years to be served concurrently
8 AR 350–100 • 8 August 2007/RAR 10 August 2009
W a s h i n g t o n , D C 2 0 3 1 0 – 0 3 0 0 . T h e J A G C c o mmis s io n e d a n d w a r r a n t o f f ic e r s w ill f o r w a r d r e q u e s ts to H Q D A (DAJA–PT), Washington, DC 20310–0300.
4–2. Exceptions
Requests for imposing ADSOs not otherwise provided herein, will be sent through Army Commands (ACOMs) or Army Service Component Commands (ASCCs), and Direct Reporting Units (DRUs) to Commander, USA HRC (AHRC–PDO–IP), 200 Stovall Street, Alexandria, VA 22332–0400 for staffing; National Guard Bureau (NGB-ARH), 111 S. George Mason Drive, Arlington, VA 22204–1373 for NG; and to The Personnel Policy and Readiness Division, 1411 Jefferson Davis Highway, Suite 3100, Arlington, VA 22202–3229 for NG AGR. Requests for imposition of an ADSO will include in the impact statement: the cost of the training, use of the officer after training, and the needs of the service (for example, shortage of the skill).
Chapter 5
Army National Guard Officer Active Service Obligation Policies
5–1. General
Linking Active Service Obligations (ASO) to graduation from senior service college assists the Army National Guard Active Guard Reserve (AGR) in effectively managing resources, while maintaining an experienced and well-qualified officer corps.
5–2. Obligations for specified programs
This policy establishes an active service obligation for Army National Guard Active Guard Reserve (AGR) officers with more than 20 years active service, who graduate from a senior service college. This new ASO policy is effective with graduates from the calendar year 2005 officer selection boards/panels.
a. Army National Guard (AGR) officers with over 20 years active service who graduate from a senior service college (including the Army War College Distance Education Program) incur a 2-year active service obligation, not to exceed their mandatory retirement date (MRD).
b. Army National Guard (AGR) officers with less than 20 years active service who are selected for attendance at a senior service college (to include the Army War College Distance Education Program) will be retained on active duty until completing 2 years of active duty following graduation from the school.
5–3. Concurrent obligations
A period of automatic active service extension based on promotion and a period of active service obligation based on graduating from a senior service college will run concurrently.
5–4. Waivers and exception
Subject to the need of the Army, the Assistant Secretary (Manpower and Reserve Affairs), or their designee may waive the automatic service extension and/or active service obligation prior to completion.

http://armypubs.army.mil/epubs/DR_pubs/DR_a/pdf/web/r350_100.pdf