You can apply for a US visa in so called "third country" if you have sufficient reasons for doing so. Does evasion from a military service while pursuing a PhD in US sounds like a valid reason for not entering home country? For example, my home country does not really care about pursuing a PhD at foreign university and can grab you any time if you are unlucky enough. I did not receive an official request to enroll there, yet, because I am, well, out of their reach :) so I am not considered criminal, nor I break any law. But I do not want to risk receiving it by visiting home country.