[R] trivial installation question

[m p]

Hello,
I try to install udunits and RNetCDF packages
With the first one
after R CMD INSTALL udunits_1.2.tar.gz the script
looks for the library, does not find and says
to edit udunits_1.0/udunits/src/Makevars.in
with links to an include file and location of the
library. When I put the correct path 
the script repeats the previous message still looking
for the library in the default path. How do I
communicate the location of libraries/include files 
to R CMD INSTALL?
Thanks,
Mark