Set Option Set by OptionSet Text

function SetValue(optionsetAttribute, optionText)
{
 var options = Xrm.Page.getAttribute(optionsetAttribute).getOptions();
 for(i = 0; i < options.length; i++)
 {
  if (options[i].text == optionText)
   Xrm.Page.getAttribute(optionsetAttribute).setValue(options[i].value);
 }
}

Calling of the function

SetValue("new_country", "India")