I think you might want to read this...
''Although a person's enlistment in the armed forces of a foreign country may not constitute a violation of U.S. law, it could subject him or her to Section 349(a)(3) of the Immigration and Nationality Act [8 U.S.C. 1481(a)(3)] which provides for loss of U.S. nationality
if an American voluntarily and with the intention of relinquishing U.S. citizenship enters or serves in foreign armed forces engaged in hostilities against the United States or serves in the armed forces of any foreign country as a commissioned or non-commissioned officer''.
http://travel.state.gov/law/citizenship/citizenship_780.html
Since Israel has engaged in hostilities against the US in the past, and given the worsening US-Israeli relations, do you really want to put yourself into the situation of risking having to be ordered to fire on your own country? If you do, then do us all a favor and renounce your US citizenship right now and save us the trouble of kicking you out later
Don't kid yourself...if it was in the Israeli national interest to fire on US forces, they wouldn't bat an eyelash to do so. They have done precisely this in the past. The sad truth is that countries that have helped Israel in the past have wound up regretting it later (UK, France, USA)...
If I might make a suggestion...if you are dead-set against serving in the US military (which IMHO is your best option), I might suggest you look at the French Foreign Legion as you don't risk a conflict of interest or risk losing of your citizenship. Note: I don't actually suggest you should actually join the FFL because its a extremely brutal life (much worse than conventional military) and you will almost certainly see combat, but it is at least an alternative without the political risks.