WASHINGTON — Former US defense secretary Donald Rumsfeld says in a new memoir that his biggest regret was not stepping down after the Abu Ghraib prisoner abuse scandal, US media reported Thursday.

In his book, Rumsfeld -- a lightning rod for criticism during his long tenure at the Pentagon -- defends his handling of the Iraq war and makes no apologies for his major policy decisions, according to advance copies obtained by the New York Times and the Washington Post.

But he said he should have forced then president George W. Bush to accept his resignation over the revelations of abuse by US military guards at the Abu Ghraib prison in Iraq.

"Abu Ghraib and its follow-on effects, including the continued drum-beat of 'torture' maintained by partisan critics of the war and the president, became a damaging distraction," Rumsfeld writes.

"More than anything else I have failed to do, and even amid my pride in the many important things we did accomplish, I regret that I did not leave at that point."

Rumsfeld ended up staying in office for another two-and-a-half years until Bush sacked him following a Republican defeat in 2006 legislative elections in which the unpopular Iraq war played a major role.

Rumsfeld argues, however, that the abuse at Abu Ghraib was the result of rogue soldiers and not policies, a stance that rights groups have rejected, citing documents and statements from senior officials.

The ex-Pentagon chief also said that the administration should have sought approval from Congress on its policies toward "war on terror" detainees, instead of sticking with a more unilateral approach favored by then vice president Dick Cheney.

But Rumsfeld makes no apologies for his approval of harsher interrogation techniques, the management of the prison at Guantanamo or the creation of military tribunals to try terror suspects, the newspapers reported.

The former defense secretary also denies that he ever rejected appeals from military commanders for more troops to invade Iraq, saying he never received a formal request, the Times reported.

Retired officers and numerous accounts of the run-up to Iraq have portrayed Rumsfeld as insisting repeatedly on a smaller force for the invasion.

The title of the memoir, "Known and Unknown," plays on his famous and much-lampooned remark about what was known about Iraq allegedly providing weapons of mass destruction to terrorists.

"There are known unknowns; that is to say, there are things that we now know we don't know. But there are also unknown unknowns; there are things we do not know we don't know," Rumsfeld said at a press conference in 2002.