For this you have to know the option values before you render the View. For example in your view
<?php echo $form->radioButtonList($model,'attribute', array('0'=>'option1 ', '1'=>'option 2 ', '2'=>'option3 ')); ?>
Then before rendering this view in you action write
$model->attribute='1';
Then option1 will be selected when the raioButtonList is rendered.Similarly you can select other options as per your needs