So you are imagining the possibility that the army or national guard would be less well equipped than a civilian?
Actually, I have a difficult time imagining a senario in which the United States is invaded out of the blue, totally unexpected. And really, I can't think of any other time that's happened. Pearl Harbor was neither an invasion or entirely unexpected. They just didn't get the word in tiime. This isn't to say that invasions are never a surprise. Generally they are planned in great secrecy but things rarely happen without a buildup of both tension and military forces. But you never know how things will turn out.
It is rare in history when unorganized resistance to anything is successful. Most instances in which guerrila warfare or semi-guerrila warfare is waged, it is done so with considerable outside assistance, generally in the form of weapons and ammunition. And many wars that people imagine are fought by "the people" are in reality being fought by organized units equipped by the government, even if it is a rebel government. That pretty well describes the Boer side in the Boer Wars. They had government issued rifles and were in organized units, even if they did not wear uniforms.
By the time old folks my age are called up, it would be a pretty desparate situation, just like was done in Germany in 1945. Me and my .30-30 would probably just as well stay home and keep out of the way.
Shoot low, sheriff. They're riding Shetlands!
Underneath the starry flag, civilize 'em with a Krag,
and return us to our own beloved homes!
Buy War Bonds.