Washington (CNN) -- If the Bush administration had known there were no weapons of mass destruction in Iraq, it probably wouldn't have decided to invade in 2003, former Defense Secretary Donald Rumsfeld said in an interview broadcast Sunday.

Speaking on CNN's "State of the Union" program, Rumsfeld noted there were multiple reasons for attacking Iraq and ousting Saddam Hussein from power.

However, intelligence reports -- now shown to have been false -- that Iraq possessed WMDs were the main reason for going in, Rumsfeld said.

"No question it was the big one," he said. Asked if the United States would not have invaded if the administration hadn't believed Iraq had the weapons of mass destruction, Rumsfeld said: "I think that's probably right."

He criticized the source known as "Curveball" -- an Iraqi defector who admitted his claims that Iraq possessed WMDs were false -- but stopped short of condemning the U.S. intelligence community.

"The intelligence community talks to hundreds of people," Rumsfeld said. "They have human assets, such as this man. Some are honest, some are dishonest. Some do it for money, some do it for self aggrandizement. Some do it, apparently, to lie."

Now peddling a book, four years after being replaced by Robert Gates as defense secretary following heavy Republican losses in the 2006 mid-term elections, Rumsfeld maintained the swagger and bravado that were his hallmarks when dealing with the media as a Cabinet member.

He said said the Obama administration was "wrong in attacking the Bush administration's structures that have kept this country safe for almost a decade now," including the detention facility at Guantanamo Bay, Cuba.

President Barack Obama campaigned on the promise that he would close the facility known as Gitmo in his first year in office, but it remains open.

"They now have switched from the campaign mode, and they are keeping Guantanamo Bay. They are keeping indefinite detention," Rumsfeld said. "They are keeping military commissions. So obviously, they've come to the conclusion that their campaign promises -- easier to campaign than it is to govern."

Rumsfeld also rejected the premise that the United States is viewed more favorably around the world with Obama as president.

"No, and I don't think there's data that supports that," Rumsfeld said. "I think he had made a practice of trying to apologize for America. I personally am proud of America."

He was also critical of the Nobel Peace Prize awarded Obama in his first year in office in 2009.

"Well, he had not accomplished a thing when he got the Nobel Prize," Rumsfeld said. "It was given to him on hope. Had to have been, because there wasn't anything that he'd done."

Despite receiving some boos when he recently was honored at the Conservative Political Action Conference, the annual gathering of conservative activists, Rumsfeld said the Tea Party movement has brought "a lot of energy into public life and public affairs."

He said he was "deeply worried about the budget" and that the country needs to start saving money now. Some of those savings can come in the Pentagon budget he formerly oversaw, he said.

"My goodness, every year the Congress was stuffing $10 billion down the Pentagon's throat that we didn't want," Rumsfeld said. "There's no question that there's money there."