Perhaps any engineers you employ are less likely to be employed by your enemies? It seems proven that greater trade between countries reduces risk of war, and employment might follow the same pattern.

Also, quite possible that your research money goes farther. If this produces greater progress per dollar, this might create greater security. But this might depend on whether you are developing offensive or defensive tools.

So if an italian has a better solution, then DARPA have failed on your point 1. because he can use that against americans (i.e block their spectrum), and DARPA won't know about it.

Citation on your point 2. Where does it say anywhere that Government can only spend it's money on employing Americans?

I am Italian (hey Volpe :-D), but I lived in the US for a little while.

I understand that what made American great is its ability to use talent from other countries, honestly US does NOT have the best scientists or engineers but it offer to the best mind the opportunities to shine, opportunities that we don't have in my country.