The US began the WWII draft over a year before Pearl Harbor, and was manufacturing arms for the Allies months ahead of Pearl Harbor as well. Even a weakened American industrial base was significantly larger than that of any other country in the world at the time (http://www.combinedfleet.com/economic.htm).

World War II was an unusual case, though. Every war since then has been a relatively limited one in the sense that no one on the home front really made any kind of sacrifice or even any substantial contribution to the war effort. In World War II, as much of the country's productive output as possible was dedicated to the war effort. Civilian consumption was strictly rationed, and the population actually went along with this. People gardened and learned to get by with less because every gallon of gasoline they didn't burn, every tire they patched up instead of replacing, every bit of food or cloth or wood or steel that you didn't needlessly consume could be shipped off to the front lines and contribute to victory. Every dollar you saved could be invested in war bonds. There was hardly a single American who lived through that war who didn't make sacrifices and materially contribute to victory.

If you were able to get that level of dedication out of the population again, you could scale an effective military force in very short order the way the US did in WWII. But that just isn't going to happen again for any foreseeable conflict.