stack overflow using step()

Hi,
I'm using step() for forward regression with 680 main effects and the
correspomding 230860 interactions. However, the calculation is stopped with the
message:
Error: protect(): stack overflow

How can I specify the maximum size of the pointer protection stack when running
R not from command line but in an emacs-subwindow?

How can I perform these calculations when the maximum value accepted is 100000?
Thanks,
Benjamin