Should automake add X_LIBS to LIBS automatically?

[address@hidden]

Hi! I'm trying automake. I can't understand why automake doesn't add
X_LIBS to LIBS automatically when it finds AC_PATH_XTRA in confgigure.in

And what's the correct way to do this manually? Either

export LIBS="$LIBS $X_LIBS"

in configure.in after AC_PATH_EXTRA or

LIBS = @LIBS@ @X_LIBS@ MY_LIBS

in Makefile.am?
Is there a  cleaner way?

TIA