The problem isn't really the experience. It's whether or not the hospital wants to train you to work in the OR or not. OR nursing is very different from any other floor nursing, thus it costs a grip of money for the hospital to train you, since nursing education generally does not provide such training. Training often includes OR procedures, setting up OR rooms, learning all the instruments, supplies, etc. My recommendation is that when you do get a OR nursing job interview is that you fully express to them your intention to stay with them (for a VERY long time)

, so that the agency will feel that their money was well invested.
Hope this helps. Currently I'm an OR nursing extern, and this is what my manager stressed before he even hired me as an extern.