His comments were in direct contradiction to earlier public statements.
Rumsfeld, widely held as the most hawkish member of the US government's inner circle, wrote that it was not possible to transform the Defence Department quickly enough to effectively fight the “anti-terrorism war”.
President George Bush seized on the overall message of the memo - that the war on “terrorism” would be long and hard - to say that he could not agree more.
“I haven't seen the secretary's comments, but somebody told me they thought he said we need to make sure our military's intelligence services are focused on the war on terror. And I couldn't agree more with you,” Bush told reporters who asked him about the memo in Canberra, Australia.
“That's exactly what we're doing,” he added.
Both the Pentagon and the White House said the memo, dated 16 October, properly raised issues for US defence chiefs to consider.
Rumsfeld, speaking to reporters after a closed briefing for senators, said the memo was an effort to raise questions.
“Sometimes one needs to say to a big institution: Hey, wait a minute. Let's lift our eyes up and look out across the horizon and say, 'Are there questions that we ought to be asking ourselves? Are there things that we ought to do differently?'” he said.
“Secretary Rumsfeld is only now acknowledging what we've known for some time -- that this administration has no plan for Iraq and no long-term strategy for fighting
Retired Army Gen Wesley Clark, a Democratic presidential candidate
He said the memo stemmed from reports he had received from combatant commanders around the world, and was sent to “three or four of my closest associates”.
In the report, he wrote it was “pretty clear the coalition can win in Afghanistan and Iraq in one way or another, but it will be a long, hard slog.”
“My impression is that we have not yet made truly bold moves, although we have made many sensible, logical moves in the right direction, but are they enough?” Rumsfeld wrote, referring to the war on terrorism.
He asked, almost rhetorically, whether the US was “winning or losing the global war on terrorism? Does the US need to fashion a broad, integrated plan to stop the next generation of terrorists?” he asked.
Some hailed the defence secretary’s comments as a welcome panacea to the rampaging rhetoric of the past.
Delaware Sen Joseph Biden, top Democrat on the Senate Foreign Relations Committee, said the memo marked “the first bit of introspection that I've even whiffed” from the Defence Department's top civilian officials.
“I'm not suggesting there's a change in direction but there's a little self-doubt setting in,” Biden said.
Retired general, Wesley Clark, a Democratic presidential candidate, said, “Secretary Rumsfeld is only now acknowledging what we've known for some time - that this administration has no plan for Iraq and no long-term strategy for fighting terrorism.”