lme and ordering of terms

Dear R users,

When fitting a lme() object (from the nlme library), is it possible to 
test interactions *before* main effects? As I understand, R 
conventionally re-orders all terms such that highest-order interactions 
come last - but I??d like to know if it??s possible (and sensible) to 
change this ordering of terms.

I??ve tried the terms() command (from aov) but I don??t know if something 
similar exists for lme() objects.

Thanks a lot for your help!

Best wishes
Christoph