RabbiOfBerlin:
1. I guess we agree the sugya in Sotah says that one should not stop a mitzvah for the sake of war. You propose that is only preventive war, if I understand you correctly. So the Sugya there is either irrelevant to our case (you consider Israel to be under actual atack. I guess we disagree about that. I think that today, 7-18-2013, we are not under actual attack.) or says that it is not considered a mitzvah.
2. The discussion is if one is already fighting: is that osek bmitzvah. On the other hand, if one is not fighting yet, but is involved in other mitzvos, osek bmitzvah would free them (in the case of Talmud Torah – only if it can be done through others)
I made this point before but I am repeating it because I sense it was not understood, certainly not addressed.
3. The Taz (if I recall correctly) writes that someone who stops learning because of a bona fide pikuach nefesh that was not efshar laasos al ydei acherim is doing what the halacha requires, yet is getting the raw deal: it would have been far better for him to have continued learning.