It is hard for people to understand the service the United States military and other agencies go through unless they some how experience it. Although the population of the United States is large there is benefit to national service and it can help people gain a level of ownership for their country that may not currently exist in this day and age.
No, national service should not be required in the United States, because we are country that was founded on the principles that we are all free. It would be against what we believe in to require service from each person. We should only work if we agree to for a price.
A massive mandate of national service would weaken the US as people who do not have an aptitude for certain disciplines will be forced into service. National service should be reserved for those who have a desire to serve - this will ensure a motivated workforce that will best serve the country's interests.
I do not believe national service should be required in the United States unless all government jobs are open for that national service, not just positions in the military. I think forcing people into the military is anti-productive because some people will not assimilate to that environment, nor do they want anything to do with the rigid structure.