How to use multiple meta values in query_post function for filter post

Hi
I need some tweak for query_post function.
I want do two things on post listing page.
task 1)i want to sort listing by start_date meta value

//
                $query[ 'orderby' ] = 'meta_value';
                $query[ 'meta_key' ] = '_ep_start';
                $query[ 'order' ] = 'ASC';
                query_posts( $query );
task 2)also only show post which have end_date is equal to or greater than todays date.
            $curdate=mktime(0,0,0,date('m'),date('d'),date('Y')) ;
            $query['meta_key']='_ep_end';
            $query['meta_compare']='>=';
            $query['meta_value']=$curdate;
            query_posts( $query );

above code is working fine. It is working fine if i use only one task at time. but when i use both, that $query['meta_***'] is overidden. so it gives result of last meta key.

i want to use multiple meta values in query_posts function. Please help me. I think this is very usefull for filtering post functionality.