Memo to Dick Cheney: Iraq had destroyed its illicit weapons stockpiles within months after the Persian Gulf war of 1991, and its ability to produce such weapons had significantly eroded by the time of the American invasion in 2003, the top American inspector for Iraq said in a report made public Wednesday. The report by the inspector, Charles A. Duelfer, intended to offer a near-final judgment about Iraq and its weapons, said Iraq, while under pressure from the United Nations, had "essentially destroyed'' its illicit weapons ability by the end of 1991, with its last secret factory, a biological weapons plant, eliminated in 1996. Mr. Duelfer said that even during those years, Saddam Hussein had aimed at "preserving the capability to reconstitute his weapons of mass destruction when sanctions were lifted.'' But he said he had found no evidence of any concerted effort by Iraq to restart the programs.