i wouldnt change my major now. i'm not completly up to date so i could be wrong, but i dont think it matters what your degree is in to enter the fbi or other fedral agency, so long as you have one. kinda like the military, in order to be an officer, you have to have college, you could have a degree in basketweaving, but it would still earn you the bars after going active. have you contacted the fbi and spoken to anyone? my friends wife is a social worker, she applied to the fbi with a masters in some sort of psycho crap. it didnt stop her. (btw, she didnt join after all) i say go for it if thats what you want to do, i'm sure your degree will come in handy at some point. good luck.
I do what I can do when I can do it.