US President Barack Obama lauded George W. Bush as resolute in the face of terrorism at the opening of a library on Thursday, which makes his predecessor's case for history.

With all living US presidents at his side, Bush admitted some of the choices he made were unpopular, but said he was driven by a mission to spread freedom during two tumultuous terms marked by the Iraq war and the Sept 11, 2001, attacks.

The dedication of the library, museum and policy center in Dallas put a capstone on Bush's political career.

Obama, who had flagrant foreign and economic policy disagreements with Bush, chose instead to highlight the 43rd president's character and spoke of a special bond with one of the few men alive who sat in the Oval Office.

"He's comfortable in his own skin. He knows who he is. He doesn't put on any pretenses ... he is a good man," Obama said.

He remembered how Bush steadied a nation traumatized by the Sept 11 attacks and began to plot the US response.

"We're reminded of the incredible strength and resolve that came through that bullhorn as he stood amid the rubble and the ruins of Ground Zero," Obama said, and also thanked Bush for his counsel when he became president.

"No one can be completely ready for this office," Obama said.

"But America needs leaders who are willing to face the storm head on. That's what president George W. Bush chose to do."

In a reference to his wild youth, Bush, 66, said, "There was a time in my life when I wasn't likely to be found at a library, much less found one."

But turning serious, he made an impassioned case that his controversial policy of pre-emptive war and regime change in Iraq was born of principle.

"When our freedom came under attack, we made the tough decisions required to keep the American people safe," said Bush, who choked up in the coda to his speech when he paid tribute to his "brave and noble" country.

The new library, on the campus of the Southern Methodist University, is stuffed with papers and artifacts of Bush's White House years, but it is the horror of Sept 11 that dominates.

A steel beam twisted in the inferno of the World Trade Center reminds visitors of the fury of the terror attacks which led the US into war in Afghanistan and Iraq and exacted a heavy human and economic price.

But Bush admits to no regrets.

Asked by ABC News whether he had any second thoughts about the 2003 invasion of Iraq, now convulsed by new violence, Bush said: "I am comfortable in the decision-making process."

Like Obama, former Democratic presidents Bill Clinton and Jimmy Carter chose to skip over controversy and praised Bush for battling AIDS in Africa.

World leaders were also in Dallas to honor their former comrade-in-arms, including UK ex-prime minister Tony Blair and former Australian leader John Howard.

Key members of Bush's administration hoped history will look kindly on their boss after he left office under a cloud of unpopularity.

Bush also had a word for his hawkish vice-president Dick Cheney, after reports that their friendship fractured during his second term.

"He served with loyalty, principle and strength," Bush said.

(China Daily 04/27/2013 page8)