How to get Sharepoint User object from the "AssignedTo" field using client side object model ?

Question

I am using managed client side object model in sharepoint 2010. And I want to get loginaName of the AssignedTo user in Task list.

In server side object model I use SPFieldUserValue.User.LoginName to get this property but in client side object model FieldUserValue.User does not exists.

How can I resolve this situation ?

Thanks