Automation paning?

What is the simplest way to automate paning? If I want a source moving from say left to right during the track?

Well, unless I am missing something, you just automate it. Like .e.g. enable write Automation on the track and move the panner with the mouse. where you want it. Or draw in the automation on the automation line like with any other automation.
Or do you mean not only once, but permanently throughout the project? You could use the autopan plugin for that. Or, for more manual control, again draw automation, but with the line tool set to sine, triangle or square.

Thanx, I am a novice so I am missing these simple things sometimes.