WASHINGTON – Former defense secretary Donald Rumsfeld releases his new memoir Tuesday, as he concedes his Iraq troop decisions may have been wrong while sparing no criticism of former colleagues.

In "Known and Unknown," Rumsfeld defends his handling of the war and recounts his government career serving Republican presidents from Richard Nixon to George W. Bush.

The former defense secretary was reluctant to endorse Bush's assessment that the decision to draw down US troops shortly after the 2003 invasion of Iraq was "the most important failure in the execution of the war."

"I don't have enough confidence to say that that's right. I think that it's possible," Rumsfeld told ABC News anchor Diane Sawyer.

"We had (an) enormous number of troops ready to go in. They had -- we had off-ramps, if they weren't needed.

"It's hard to know. You know, the path you didn't take is always smoother," he added.

The former Pentagon chief's comments came in his first television interview since leaving public life in December 2006 after a long and divisive tenure at the Pentagon.

They largely echoed his memoir, in which he laid blame for much of the failings and heavy bloodshed of the Iraq war on "too many hands on the steering wheel."

Rumsfeld, who served as Bush's defense chief for six years after holding the the same job under president Gerald Ford in the 1970s, acknowledged that "in a war, many things cost lives."

But he had no regrets about his leadership of the wars in Iraq and Afghanistan -- the latter now nearing its 10th anniversary.

He refused to echo the regrets of another domineering defense secretary -- the late Robert McNamara -- who came to describe the Vietnam War as "terribly wrong."

"That's not the case with Iraq," Rumsfeld countered.

"I think the world's a better place with Saddam Hussein gone and with the Taliban gone and the Al-Qaeda out of Afghanistan," he added, insisting the Bush administration's decision to invade Iraq in the wake of the September 11, 2001 attacks on the United States was "incremental," not rushed.

Rumsfeld said it was Paul Wolfowitz, then a deputy secretary of defense and later a major architect of the Iraq war, who raised Iraq at the Camp David presidential retreat shortly after 9/11.

Just as in his book, the former defense chief also ripped into some of George W. Bush's closest advisers, saying Condoleezza Rice lacked experience and Colin Powell showed poor management skills.

Asked whether he admired his ex-boss's father president George H.W. Bush -- under whom he did not serve -- Rumsfeld replied curtly: "No, I was kind of disappointed in him."

Rice, Bush's national security adviser who later became secretary of state, had "never served in a senior administration position," a lack of experience that hampered her ability to organize critical meetings, Rumsfeld said.

He said Powell -- Bush's first top diplomat -- "did not, in my view, do a good job of managing the people under him," calling leaks out of the State Department "unhelpful."

Rumsfeld said Powell, along with other top Bush advisers and officials, truly believed Saddam Hussein had weapons of mass destruction when he made a presentation to the UN Security Council in February 2003 -- and never spoke up during meetings with the president to raise objections about the war.

"There's a lot of stuff (in) the press that says Colin Powell was against it. But I never saw even the slightest hint of that," he said.

On the weapons of mass destruction that never surfaced despite being cited by the Bush administration as the primary justification for the war, Rumsfeld acknowledged: "My goodness, the intelligence was certainly wrong."

But he categorically refused to to say whether he would have acted differently had he known then what he knows now about Saddam's alleged weapons.

"I have no idea. I have no idea," he said. "What you know today can help you on things you're thinking about tomorrow. It can't help you with things you were thinking about back then. Back then, there was reasonable confidence that he had these weapons."

In conjunction with bookstores selling his memoir this week, Rumsfeld is also releasing online a wide range of nearly 2,000 documents from his tenure in public service, dating back to his years as a congressman in the 1960s. They will be available on www.rumsfeld.com.