I'll make this fairly short--I have been offered a position at National Archives which requires me to obtain a Top Secret security clearance (as told to me by the woman who selected me for the position). I have smoked marijuana--at some points in my life very frequently (several times a week, several a day). I stopped about 2 months ago and have severed contact with everyone I have ever smoked with. I have no interest or intentions of smoking again, but I'm wondering if I am screwed because of the small amount of time that has passed between me quitting and this security clearance. 

Should I take this polygraph, or if I do and fail, will I be screwed for life?

Well, do you think this will be an automatic disqualification issue? Should I even bother sitting here at my computer filling out 10 years of history to be ruled out automatically for something as trivial (to me) as this? I'm on the edge about one thing: spend the time doing the paperwork to possibly be rejected and have a note made so that all future employers will be able to see or just call it quits now. 

Thanks for the reply, but it's hard for me to think of a scenario where the interviewer accepts my honest thoughts on drug use and my commitment to not using any in the future and lets it go.