[jQuery] appending an option to select list (dropdown), making it the selected one

[LinkGuru]

With the following code, I'm managing to append to a drop-down list
using jQuery, but can't figure out how to amend one of the existing
items in the drop down so it is not the selected one i.e. I only want
the one that's appended to be the selected one.
Can anyone help?
Here is the simplified code.

                $(".actionOptAdd").bind("click",
                        function()
                        {
.
.
.
                                $.getJSON('lib/addToProj.php',
                                {....}, function(data)
                        }, function(data)
                                {
                                   $.each(data, function(i,item)
                                   {
                                            if ( i == "project" )project=item;
                                            if ( i == "insertid" )insertid=item;
                                   });
                                   var drp = $('#dropdown');
                                   drp.append("<option value='"+insertid+"'
selected='selected'>"+project+"</option>");
                                   });
                        }
                );
//Thanks in advance.