In his first extensive remarks about a recent U.S. intelligence report saying the threat of terrorism has risen, Rumsfeld told reporters at a NATO meeting that, in general, the value of intelligence reports can be uneven, and "sometimes it's just flat wrong."
But he added that "the implication that if you stop killing or capturing people who are trying to kill you, then therefore the world would be a better place, is obviously nonsensical."
His statements came a day after the White Houseof a secret intelligence assessment that depicts a growing terrorist threat.
In the much-discussed National Intelligence Estimate initially reported last weekend, the government's top analysts concluded that Iraq has become a "cause celebre" for jihadists, who are growing in number and geographic reach. If the trend continues, they said, the risks to the U.S. interests at home and abroad surely will grow.
Rumsfeld did not specifically criticize or address the controversial intelligence report, but instead commented more broadly about the terrorist question that has gripped the political world since the report was disclosed last week.
"Are more terrorists being created in the world? We don't know. The world doesn't know," said Rumsfeld, adding that there are no good ways to measure "how many terrorists are being trained at camps around the world."
Disclosure of the classified report, and U.S. President George W. Bush's subsequent move to make public portions of it, has had broad political ramifications.
For Republicans, the report provides more evidence that Iraq is central to the war on terrorism and can't be abandoned without giving jihadists a crucial victory. And for Democrats, it furthers their argument that the 2003 Iraq invasion has inflamed anti-U.S. sentiment in the Muslim world and left the U.S. less safe.
Rumsfeld said any specific comments on the report should come from Bush. But he added that while it's hard to know how many terrorist are being created, officials have a better idea how many have been killed or captured.
On Thursday the new leader of al Qaeda in Iraq purportedly said in an audio message posted online that more than 4,000 foreign militants have been killed in Iraq since the U.S.-led invasion in 2003 — the first apparent acknowledgment from the insurgents about their losses.
Rumsfeld also said there are multiple groups of extremists whose goal is to murder and terrorize free people and their goal is to topple any Muslim regime that disagrees with them and replace them with extremists.
"Ultimately they will fail," said Rumsfeld, adding that "anyone who thinks there is a single answer or a single reason, or a silver bullet that's going to solve the problem can't be right, it's too complex. ... It's going to take time and it's going to take a lot of work by people who are patient and believe in freedom."
To Paul Pillar, who produced National Intelligence Estimates on terrorism during his years at the CIA, this latest estimate answers a question Rumsfeld asked in an internal memo nearly three years ago: Is the Muslim world turning out terrorists faster than the United States can kill or capture them?
Pillar tells CBS News national security correspondent David Martin that the recent NIE report answers Rumsfeld's question.
"With particular reference to the impact of the Iraq war, the unfortunate answer is yes, we are creating them faster than we capture or kill them," Pillar, who is a former national intelligence officer for the Near East and South Asia, says.
Rumsfeld was attending a NATO defense ministers meeting here. During the meeting, the ministers approved extending NATO's control of military operations across all of Afghanistan — a move that Rumsfeld hailed as a "bold step forward" for the alliance.
Under the new arrangements, as many as 12,000 additional American troops will be put under foreign battlefield command, a number that U.S. officials said could be the most since World War II.