Not (quite) true. Clarke came very lose to recommending just that in his Millennium Plot after action report. Did Clarke not want to draw attention to that document? Did he know at the time of this testimony that Berger had attempted to filch and destroy copies of it?
You mean Sandy "Chuckles" Berger - "A little song, a little dance, a bunch of secrets down my pants."
Most likely he knew what Berger was up to and avoided mentioning the document