I work for the federal government (DoD to be exact). The salaries are negotiable--but as someone mentioned, there are "pay bands" that they have difficultly exceeding. An important question to ask is what "pay schedule" you are on (GS, DB, etc)--some offer more flexibility than others.
The guvment isn't known for paying their people extremely well (I'm not compared to corporate jobs)--but I do work EXACTLY 40 hours a week and have extremely nice equipment to work with. The benefits aren't as good as you would think (don't let them convince you otherwise). And if there is a security clearance requirement and you're being hired for a professional-level job, FULLY expect it to take them four months after the initial offer for you to start work and another six for your clearance to allow you to do your entire job.