According to Reuters, the Oscar-winning actor submitted an open letter urging the president to stop a cycle where "bombing is answered by bombing, mutilation by mutilation, killing by killing."
"I beg you, help save America before yours is a legacy of shame and horror," Penn said in the letter.
Penn, 42, quoted Bush's declaration that the world was either "with us or against us" in the war on terrorism launched after the Sept. 11, 2001, attacks, and said Bush was marginalizing critics, manipulating the media and promoting fear.
Those actions and "your administration's deconstruction of civil liberties all contradict the very core of the patriotism you claim," Penn added.
"Sacrificing American soldiers or innocent civilians in an unprecedented preemptive attack on a separate sovereign nation may well prove itself a most temporary medicine," he said.
The letter was signed, "Sincerely, Sean Penn, San Francisco, California."