There is much more to the answer than just a simple "yes" or "no". For example, quality of the instructor, goal of both the instructor and student, and even styles of Judo factor in the equation.
But a general answer is, "Yes, it can be." If self defense is your primary objective, I recommend tracking down a Kodokan styled dojo.
[This message has been edited by SB (edited June 10, 2000).]