post order : descending years, ascending months

Hi, I’d like to have my post order by year:

2013, 2012, 2011, etc.

but the month ordered in a given year:

January, February, March, etc.

Can this be done?

I’ve tried modifying index.php, just before the line:

<?php if (have_posts()) : ?>

by adding:

<?php query_posts($query_string . ‘&orderby=date&order=ASC’); ?>

before it, but it just makes everything ascending…

Thanks for your time.

Thanks for any help you can provide.