President Obama announced the withdrawal yesterday of more than 90,000 US combat troops from Iraq by August next year but his decision to keep a force of up to 50,000 was attacked by leaders of his party as a betrayal of his promise to end the war.

Mr Obama's drawdown plan was even embraced by Republicans — including John McCain, his election opponent last year — but was criticised by anti-war liberals.

It was the latest of several moves by the President that have disappointed the Left, who had convinced themselves that he would end the US presence in Iraq at a stroke.

In a speech to Marines at Camp Lejeune in North Carolina, which addressed American diplomacy in the Middle East and the future of Iraq, Mr Obama declared: “Let me say this as plainly as I can: by August 31, 2010, our combat mission in Iraq will end.”

Pentagon officials said Mr Obama had decided to pull out at least 92,000 of the 142,000 troops now there. Yet he announced, as he had promised on the campaign trail, a “transitional force” to train Iraqi troops, protect civilians and hunt down al-Qaeda.

It was the size of that force — between 35,000 and 50,000 — that dismayed many Democrats.

Nancy Pelosi, the House Speaker, was clearly upset, saying she could not see how 50,000 troops could be justified. Harry Reid, the Democratic Senate Leader, and Charles Schumer, another leading Senate Democrat, also expressed displeasure.

The strategy has been agreed on by Robert Gates, the Defence Secretary, General David Petraeus, the Middle East commander, and General Ray Odierno, the Iraq ground commander. President Obama also notified the former President, George Bush.

On the issue of Iraq, where the hard-fought gains have cost so many lives, Mr Obama can accept being accused of caution by his own party. The support from the Right gives him cover as he tries to end the war.

Acknowledging indirectly the success of the “surge” of additional troops ordered by Mr Bush — a policy he opposed — Mr Obama told the Marines: “Thanks in great measure to your service, the situation in Iraq has improved. Violence has been reduced substantially from the horrific sectarian killing of 2006 and 2007.”

Yet he warned: “There will be difficult days ahead. Violence will continue to be part of life in Iraq.”

Not made explicit in the speech was the amount of flexibility in the plan. First, few troops will be withdrawn until after December's parliamentary elections in Iraq.

Mr Gates also called the August 31 deadline next year a “way station”, an indication that it could be shifted. Under an agreement between the US and Iraq, all US troops must be out of Iraq by the end of 2011.

Yet Mr Gates also indicated that a new agreement with the Iraqis was not out of the question.

John McHugh, the top Republican on the House Armed Services Committee, said that he had been assured by Mr Obama that if the security situation deteriorates, the President had a “Plan B” and would revisit the withdrawal plan.

Mr Obama said his ultimate goal was “an Iraq that is sovereign, stable and self-reliant”. He said that the US would intensify diplomatic efforts in the region to help to achieve that goal, including talks with Syria and Iran, whom he indirectly accused of “working to undermine Iraq's security”.

He added: “The future of Iraq is inseparable from the future of the broader Middle East ... We can no longer deal with regional challenges in isolation.” Mr Obama also promised more aid for displaced Iraqis and, in a direct message to the Iraqi people, he said: “Ours is a bond forged by shared bloodshed.”

He added: “Let me be clear about America's intentions. The United States pursues no claim on your territory. We can build a lasting relationship founded upon mutual interests and mutual respect as Iraq takes its rightful place in the community of nations.”

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