Well, it would be easier if the code were cleaner to begin with, but
print ("<td bgcolor=\"white\">".add('<select name="co_aut'.$i.'_country">
<option value="" '. ($_SESSION['POST_VARS']['Country'] == "" ? " selected":"").'>- Select a Country -</option></select>')."</td>");
seems to be the closest in spirit to how you're writing it.