I have found the following solution for this problem.
You can use the following url link to open the form and set a field:
<b>http://host/path.nsf/form?openform&fieldname =fieldvalue. </b>
<b>The field that should a default value of : <pre>@UrlQueryString(“fieldname”)</pre> </b>
This will set the field value first time the url is clicked. If you have many url link that passes different options to the same radio button will not work. What I need to change to be able to change field default value before click on the url link (changing default value dynamically)????