It's fairly simple. You can add multiple values to your data field data: "page"+page+"&a="+a Treat it like a as far as the formatting, meaning separate each data set by a '&' that will allow you to send multiple data values to the server in your ajax.
$.ajax
({
type: "POST",
url: "load_data.php",
data: "page"+page+"&a="+a,
success: function(msg)
{
}
});