It sort of depends. I worked for the DoD for the first three years of my post-college career. While most of the folks I met were very devoted and hard-working there were some notorious slackers (just as there are in any organization). The difference is that it's easier to cut loose the deadwood in most private orgs than it is in a federal agency, so the layabouts tend to hang on longer there....
I worked for the Navy for nine years (well, some of that was on/off as an intern).
Yes, there were dedicated, hard working people, but there were a lot of slackers. The problem is that the government actually encourages slacking and punishes anyone with motivation who cares about their work.
When you work for the DoD, no matter what you do, there is at least one group (probably more) in an independent chain of command that is essentially dedicated to seeing that you do not get your job done. As a result, no one is ever blamed for failure to get anything done because there are SO many obstacles in place.
On the other hand, fuck-ups are serious business for you, and more importantly, your management chain.
This severe punishment for screwups coupled with no expectations of success breeds an environment where just not doing anything is not only acceptable, but actually preferred.
For the first few years, it's kind of amusing. It's kind of like living the movie "Catch-22". After a while, it gets soul crushingly depressing.