Can a load bearing beam be offset from lapping joists?
You've essentially got a column buckling problem here. Factors affecting the maximum load include the geometry of the beam cross section, its material properties, and the manner which its ends are constrained. You can read up on it here.

What makes it more complicated is a possible eccentric loading condition, as The Evil Greebo points out. Now you have to worry about compressive stress and normal stress. This eBook does a good job describing the loading conditions and resulting stress under the "Maximum Stress" section. 



Since the current exact loading conditions are unknown, and in addition you're changing the location the load is applied in, I think it would seek professional engineering advice. (I would, and I'm a mechanical engineer - I just don't specialize in architecture.) Either that, or an experienced contractor may be able to give you a better answer. (Shirlock, where are you on this one, buddy?)