Former US homeland security chief Tom Ridge charges in a new book that top aides to then-president George W. Bush pressured him to raise the "terror alert" level to sway the November 2004 US election.

Then defense secretary Donald Rumsfeld and attorney general John Ashcroft pushed him to elevate the color-coded threat level, but Ridge refused, according to a summary from his publisher, Thomas Dunne Books.

"After that episode, I knew I had to follow through with my plans to leave the federal government for the private sector," Ridge is quoted as writing in "The Test of Our Times: America Under Siege ... And How We Can Be Safe Again."

Some of Bush's critics had repeatedly questioned whether the administration was using warnings of a possible attack to blunt the political damage from the unpopular Iraq war by shifting the debate to the broader "war on terrorism," which had wide popular appeal.

Fran Townsend, Bush's homeland security adviser at the White House, disputed Ridge's account, saying: "There was never a discussion of politics in the terror alerts discussions in the four and a half years I was there."

Ridge, a former governor of Pennsylvania, was the first secretary of the US Department of Homeland Security that the US Congress created in response to the September 11, 2001 terrorist strikes.

He also says that Townsend called his department ahead of an August 1, 2004 speech to ask Ridge to include a reference to "defensive measures ... away from home" -- language that he read as being a reference to the Iraq war.

In those remarks, Ridge said he was raising the threat alert level for the financial services sector in New York City, northern New Jersey, and Washington DC, and went on to praise Bush's leadership against extremism.

"The reports that have led to this alert are the result of offensive intelligence and military operations overseas, as well as strong partnerships with our allies around the world, such as Pakistan," said Ridge.

"Such operations and partnerships give us insight into the enemy so we can better target our defensive measures here and away from home," he said at the time.

He later publicly acknowledged that much of the information underpinning the new alert was three years old, stoking Bush critics' charges of political manipulation.

Townsend said that Ridge had sent her his remarks in advance of the speech and asked that she forward them around the White House for comment, and that he was free to disregard such the advice.

"The only reason I saw his words is that he sent them to me, and asked that I circulate them for comment," she said. "It was up to him, ultimately, what he was going to say."

But Democratic Senator Frank Lautenberg, a frequent critic of the color-coded alert system, said Thursday that Ridge's book "confirms our worst suspicions."

"Just like they did in Iraq, the Bush Administration manipulated intelligence to cause fear in the public to further its political goals," he said in a statement.

Ridge also details his frustration after the White House rejected his suggestion to establish department of homeland security offices in major cities such as New York, Los Angeles, Chicago, Washington, and -- long before Hurricane Katrina -- New Orleans, according to the summary.

He also says he urged his successor, Michael Chertoff, to reconsider the appointment of Michael Brown as the head of the Federal Emergency Response Agency (FEMA), whose response to the killer storm drew widespread criticism.

Ridge also charges that he was often "blindsided" during daily morning briefings with Bush because the FBI withheld information from him, and says he was never invited to sit in on National Security Council meetings.

The book goes on sale September 1.