JavaScript - Using variable to set radio button active - Need some help . .

Hello:

I have a script such as this:

   var dialogComm01 = {
   initialize: function(dialog) {
   dialog.load({"comm":this.strComm});
   dialog.load({"rd1": true});
   this.ServArea = true;
   dialog.enable({
      "rd1" : this.ServArea,
      "rd2" : this.ServArea,
      "rd3" : this.ServArea,

The first radio button "rd1" is the default.  I would like to set the default via a variable or global variable instead which might be rd2 or rd3 etc. such as like this:

   var dialogComm01 = {
   initialize: function(dialog) {
   dialog.load({"comm":this.strComm});
   dialog.load({global.defSA: true});
   this.ServArea = true;
   dialog.enable({
      "rd1" : this.ServArea,
      "rd2" : this.ServArea,
      "rd3" : this.ServArea,

But it does not fly.  Any direction would be greatly appreciated.

Thanks;

Nick