show only specific category’s post on index.php but won’t update?

hello,

i am using this code:

<?php if (is_home()) {query_posts("cat=3");}?>
		<?php if(have_posts()): ?>
			<?php while(have_posts()) : the_post();?>

	  		<div class="post" id="post-<?php the_ID(); ?>">
		  			<div class="title">
		  			<h2><a href="<?php the_permalink(); ?>" title="Permanent link to <?php the_title(); ?>"><?php the_title(); ?></a></h2>
					<?php the_time("M"); ?> <?php the_time("d"); ?>, <?php the_time("Y"); ?>
	  				<span class="comments"><?php edit_post_link('Edit Post', '<span class="editlink">', '</span>'); ?>		</span>
		  		</div>
	  			<div class="entry">
	  				<?php the_content('Read the rest of this entry &raquo;') ?>
					</div>

to show only posts that are in category “3” on my homepage.

this works great until i noticed when i click at the bottom to see previous entries…it just shows the same results over and over again.

it appears that this line is causing the problem. works fine when i remove it but the results are wrong.

<?php if (is_home()) {query_posts("cat=3");}?>