<?php
      $sort= $_GET['sort'];
      if($sort == "A")
      {
      $order= "order=DESC";
      }
      if($sort == "B")
      {
      $order= "order=ASC";
      }
?>

    <a href="?sort=A">Descending</a>
    <a href="?sort=B">Acsending</a>

<?php query_posts($order. '&cat=3&post_type=page&orderby=title' );