JOHN KERRY set a goal of withdrawing American troops from Iraq within four years yesterday as he launched his fiercest attack yet on President Bush’s “catastrophic” conduct of the war and its aftermath.

Mr Kerry, hoping the deteriorating security in Iraq will help to reverse his slide in the polls, said that his opponent's “stubborn incompetence” had led to a disaster “of historic proportions”.

The President was hiding the truth, said Mr Kerry, warning that Americans faced “a war without end” unless Washington changed tack urgently.

Mr Kerry met head-on what is fast becoming the central question of the US presidential campaign — whether Americans would be made safer by changing leader in the middle of a war. “It is not a question of staying the course but of changing the course,” he said, unveiling a four-point plan he said would secure the return of American forces to the US, starting next summer and ending in 2008.

Mr Bush hit back immediately, accusing his Democratic challenger of “twisting in the wind”. Mr Kerry’s policy, he said, amounted to “beat and retreat”. And he pounced on an assertion by Mr Kerry that, knowing what he now knows, he would not have gone to war to topple Saddam Hussein. “Incredibly, he now believes our national security would be stronger with Saddam Hussein in power and not in prison,” said Mr Bush, earning a chorus of boos from Republican supporters in New Hampshire where he was campaigning.

“He’s saying he prefers the stability of a dictatorship to the hope and security of democracy. I couldn’t disagree more.”

The Republican high command accused Mr Kerry of “the mother of all flip-flops”.

With exactly six weeks to polling day, Mr Kerry used an address at New York University to open a new line of attack, seeking to tie the bloodshed of the Iraqi insurgency directly to Mr Bush’s character.

“His miscalculations were not the equivalent of accounting errors. They are colossal errors of judgment, and judgment is what we look for in a president,” the Democratic challenger said.

Mr Kerry was trying to get on to the front foot after five weeks in which he has slipped dangerously behind in the polls. Democratic strategists have sensed a political opening created by the new spate of killings and kidnappings in Iraq. They are putting Mr Bush under intense domestic pressure.

And four senior Republicans led by John McCain and Richard Lugar, the chairman of the Senate Foreign Affairs Committee, have also turned their fire on the White House, warning that the US was in a mess in Iraq, blaming the Administration for incompetence, criticising it for not being honest with the American electorate and warning that urgent action was needed before it was too late.

Mr Kerry, who has frequently struggled to sound coherent on Iraq, was also trying to lay to rest some of the inconsistencies that have dogged his presidential progress.

He insisted that he and other senators had been right to give Mr Bush authority to challenge Saddam Hussein with the threat of force. But he said that Mr Bush had rushed to war recklessly and without a sufficiently broad coalition, and had made the US more vulnerable to attack.

He said Saddam deserved “his own special place in Hell”. And he sought to fend off criticism that he was preparing to cut and run, insisting that terrorists were beyond reason and that he would do everything to destroy them. But he tried once and for all to provide an answer that has so far eluded him about how he would have acted differently from Mr Bush.

Mr Kerry, referring to the President, said: “Is he really saying to Americans that if we had known there were no imminent threat, no weapons of mass destruction, no ties to al-Qaeda, the United States should have invaded Iraq? My answer is resoundingly no because a commander-in-chief's first responsibility is to make a wise and responsible decision to keep America safe.

“Saddam Hussein was a brutal dictator. But that was not, in itself, a reason to go to war. The satisfaction we take in his downfall does not hide this fact: We have traded a dictator for a chaos that has left America less secure.”

But Mr Kerry’s assertion was a gamble, especially in a week when Mr Bush is hosting the Iraqi interim Prime Minister Iyad Allawi, the most vivid symbol of post-Saddam Iraq, at the White House. Mr Kerry had barely finished speaking when Republican chiefs accused him of changing his position yet again, pointing out that during the Democratic primaries Mr Kerry had criticised Howard Dean for saying the capture of Saddam had not made the US safer, a position he was now espousing himself. Mr Kerry's four-point plan included securing more help from other nations, stepping up the training of Iraqi security forces, providing more tangible benefits to the Iraqi people and ensuring that democratic elections were held in Iraq in January as planned. None are goals that Mr Bush would particularly disagree with. But Mr Kerry stressed the urgency required.

He said 42 Americans had been killed in Iraq in June, 54 in July, 66 in August and 54 so far in September, saying that without action the US faced a growing insurgency and a wider war zone.

His new, increasingly confrontational tone follows the influx of half a dozen senior aides, many of them from the Clinton Administration, advising him how best to get on the front foot.

• The campaigns of Mr Bush and Mr Kerry have tentatively agreed to three face-to-face debates, a source familiar with the negotiations said yesterday.

  The debates, beginning on September 30, could prove pivotal in the contest and in an effort to lower voters’ expectations, each side in recent weeks has begun to portray the other as having the stronger debater.
  
  EXIT STRATEGY

  John Kerry’s four-point plan for Iraq:

• Commit more nations to help America in Iraq
• Provide better training for Iraqi security forces
• Provide benefits to the Iraqi people
• Ensure that democratic elections can be held next year

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