The army was constantly training up people and producing machines, but rather than load them on boats and send them overseas they'd just turn the around and stick em on trains heading toward whatever inland fighting was needed.
I think a more serious issue would be the lack of officers in the Captain-Major-Colonel rolls. Most of the instructors would have been Sgt. so for at least a while the noncom ranks would be at least decent.
A lot of the training done for the North-Africa/Italian campaign was done in the UK, but later in the war training had shifted and troops were getting most of their training in the USA before shipping out.
I don't know how many National Guard units, or what percentage (very high I suspect), but in Feb 10 of 1941 a lot of the upper-midwest National Guardsmen were put under Federal command and sent to do preparation training as part of the 34th "Red Bull" infantry division. So yes, they were mobilizing before Pearl Harbor. The current Minnesota National Guard has been very active in Iraq and Astan - the 1st brigade combat team of the 34th is the longest serving unit in this very long war.
ANYWAYS, they do have a training camp here in MN that was built right around 1930, so I imagine most regions would have an active National Guard base, but these bases would be training up new troops to send in as regular Army not National Guard. I'd put the military force for this as well equipped (with equipment fresh off the assembly lines) but very green and lacking in mid-level leadership. Early in the war the troops would be training on the old 1903 springfield, but that late in the war the Army was training with the M1 Garand from day one.
Of course in such an event I suspect a lot of WW 1 veterans would step up to fill those voids in mid-level leadership. Heck in addition to the very green well equipped troops you could have groups of 'old men' who have slower movement but improved moral and marksmanship etc.
And then there's always the regular 'citizens militia' of every red blooded American grabbing his rifle or shotgun and rallying to repel invaders. I speculate that these groups would be organized and lead by the local sheriffs.