Details here; an excerpt:

If a new draft law is enacted, the government could start sending new recruits to military training very quickly. The reason: Former President Jimmy Carter put the framework of the current Selective Service system in place in 1980. Although Carter never activated it, as part of the framework, young men must register with the government when they turn 18.

That means…that new recruits could be sent to boot camp within two weeks of the draft law’s passage….

Charles Pena, director of Defense Policy Studies at the Cato Institute, a conservative Washington-based think tank, does not see a military draft in the future. Instead, he said, the federal government is more likely to require compulsory national service.

"We won’t have a draft like we had in the Vietnam era," Pena said. "There are two important stumbling blocks to bringing that back. First, what do you do about women? They weren’t drafted before but are now an important part of the military. Second, what happens if someone who is drafted says that he or she is a homosexual?"

There is no groundswell for national service legislation now, Pena said, but it is being discussed by lawmakers and at policy seminars throughout the nation’s capital.

"It’s lurking right below the surface. There are enough people willing to get behind it on Capitol Hill that it’s something that could be done. Right now no one’s pushing for it, but just as importantly, no one’s pushing against it," he said.

Under national compulsory service, no one would be exempt, he said. People could join the military or perform some other form of community service, Pena said.