conditionally using libtool

[Bob Rossi]

Hi,

I would like to have my package create a single static library and a
single program by default.

However, if the user does --enable-tcl-extension, then I would like to
create a shared library using libtool.

Can I do something in configure.in that says 
  if .. 
    AM_LIBTOOL
  fi;

or is this invalid?

Thanks,
Bob Rossi