mymodule.php

<?php
function mymodule_form_alter(&$form, &$form_state, $form_id)
{
    if($form_id == 'views_exposed_form' && $form['#id']=='views-exposed-form-mitarbeiter-page-1' ) {
      //Items per page
      $form['#info']['filter-items_per_page']['operator']= 'items_per_page_op';
      $form['#info']['filter-items_per_page']['value']= 'items_per_page';
      $form['#info']['filter-items_per_page']['label']= t('Items per Page');
      $items_per_page_ar = array ('10'=>'10','20'=>'20','30'=>'30','50'=>'50','100'=>'100',''=>'alle');
      $form['items_per_page'] = array();
      $form['items_per_page']['#type']='select';
      $form['items_per_page']['#options'] = $items_per_page_ar;
      $form['items_per_page']['#multiple'] = FALSE;
      $form['items_per_page']['#size'] = 1;
      $form['items_per_page']['#default_value'] =10;
      }      
 }
?>