HINT: Use separate LIMIT and OFFSET clauses Código PHP:
$_pagi_result = pg_query($connection,"SELECT *from materiales ORDER BY descrip_mat DESC OFFSET $_pagi_inicial LIMIT $_pagi_cuantos");
Te sugiero que revises este paginador:
http://www.jvmultimedia.com/home/art...p?articleId=18
Saludos