WASHINGTON (Bloomberg) — Former Federal Reserve Chairman Alan Greenspan said in his new book that the Iraq war "is largely about oil," an assertion disputed by lawmakers and the US defense secretary.

"I'm saddened that it is politically inconvenient to acknowledge what everyone knows: The Iraq war is largely about oil," Greenspan, 81, wrote in "The Age of Turbulence: Adventures in a New World."

In a chapter devoted to energy, Greenspan wrote that the attention given by developed nations to the political situation in the Middle East is directly tied to oil security.

"Whatever their publicised angst over Saddam Hussein's `weapons of mass destruction,' American and British authorities were also concerned about violence in an area that harbours a resource indispensable for the functioning of the world economy," he wrote.

The book, an advance copy of which was obtained by Bloomberg News, is scheduled for publication today. The Sunday Times in London earlier published an account of Greenspan's view of the war on its Web site.

Greenspan's remarks may reinforce the views of some anti-war groups that have accused President George W. Bush and Vice President Dick Cheney, both of whom had worked in the oil industry, of pushing for war because of their ties to energy companies.

Defense Secretary Robert Gates rejected the idea that oil was a reason for the US-led invasion of Iraq in March 2003.

"What we were going after was an aggressive dictator who was a destabilising force in the entire region," Gates, who became the defense chief last December, said on ABC's "This Week" programme yesterday. "I know the same allegation was made about the Gulf war in 1991, and I just don't believe it's true."

Before the war, Iraq supplied on average 800,000 barrels of crude oil a day to the US, or about 8.6 percent of total US crude oil imports, according to the US Energy Department. That made it the sixth-largest supplier to the US, after Saudi Arabia, Mexico, Canada, Venezuela and Nigeria.

Gates said the invasion was intended to prevent Hussein from developing weapons of mass destruction or expanding earlier stockpiles. No biological or chemical weapons were found in Iraq after Hussein's regime was toppled.

Democratic Senator Evan Bayh of Indiana, who was a member of the intelligence committee when Bush sought authorisation to use military force against Iraq, said there was no suggestion in briefings that oil supplies were a rationale for going to war and it wasn't a consideration for lawmakers.

"For the members of Congress who voted at that time, it was about a belief that there were weapons of mass destruction that Saddam was seeking," Bayh said on CNN's "Late Edition" programme. "That turned out to just simply not be the case, but that was what was motivating most of our thinking."

Republican Senator John Cornyn of Texas said on the same programme that 77 senators wouldn't have voted for the war "if it was only about oil. This is about our national security."