It would be difficult, even if you are very disciplined.
I started my master's program while I was working full time as a high school teacher. Even taking one class a semester, the 200-300 pages a week of reading was difficult on top of the 40 hour work week. After 5 years of a class here and there, I decided to quit my job so that I could focus on school full time.
The benefit of working of course is that you can pay as you go. In the end it might be best to weigh the costs and benefits of either route, the amount of debt you would take on to get the degree versus the earning potential after you finish.