WASHINGTON, Dec 1 (Reuters) - President George W. Bush said the biggest regret of his presidency was flawed intelligence that Iraq had weapons of mass destruction and told ABC "World News" in an interview airing on Monday that he was unprepared for war when he took office.

Bush leaves the White House on Jan. 20 with public approval ratings near record lows partly due to the unpopular Iraq war that toppled Iraqi leader Saddam Hussein after the U.S.-led invasion in March 2003. More than 4,200 U.S. troops have died in Iraq.

"The biggest regret of all the presidency has to have been the intelligence failure in Iraq. A lot of people put their reputations on the line and said the weapons of mass destruction is a reason to remove Saddam Hussein," Bush said.

But he declined to speculate on whether he would have gone to war if the intelligence had said Iraq did not possess weapons of mass destruction.

"That's an interesting question. That is a do-over that I can't do," Bush said, according to excerpts from the recent ABC interview at Camp David.

As he prepares to hand over wars in Iraq and Afghanistan to successor President-elect Barack Obama, Bush said the issue he was most unprepared for when he became president was war.

"I think I was unprepared for war. In other words, I didn't campaign and say, 'Please vote for me, I'll be able to handle an attack'," Bush said. "I didn't anticipate war."

Pulling U.S. forces out of Iraq before the appropriate time would have compromised his principles, he said.

"It was a tough call, particularly, since a lot of people were advising for me to get out of Iraq, or pull back in Iraq," he said.

There are 146,000 U.S. troops in Iraq and 32,000 in Afghanistan.

In his final months at the White House, Bush said he was required to take bold action on the financial crisis to ward off another Great Depression.

He was asked whether it scared him that government actions to address the financial crisis amounted to about $7.5 trillion, equivalent to about half the U.S. economy.

"What scared me is not doing anything, which would have caused there to be a huge financial meltdown and the conceivable scenario that we'd have been in a depression greater than the Great Depression," Bush said.

He told ABC: "I will leave the presidency with my head held high." (Reporting by Tabassum Zakaria; Editing by Cynthia Osterman)

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