President George Bush wants to speed up the withdrawal of American combat troops from Iraq, a move that could help to quell the anti-war anxieties of voters before November's presidential election.

Drawing down large numbers of troops would enable the Republican candidate, John McCain, to say that his forceful military strategy for Iraq was correct. Alone among Republican and Democratic politicians, he consistently urged Mr Bush to take on the insurgents with extra forces. He is now attacking his Democratic opponent, Barack Obama, for preaching policies of defeat by calling for a withdrawal in 16 months.

American commanders want to reduce their deployment in Iraq to ease the strain on the military and free up troops for Afghanistan where they are taking a beating from the Taliban and other militants.

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Nine American soldiers were killed and 15 wounded yesterday in the bloodiest day in three years for US forces in Afghanistan. In a multi-pronged attack, revealing sophistication and daring, militants overran a remote US base near the Pakistan border on the front lines of the hunt for Osama bin Laden. It was the deadliest on US forces in the country since 16 combat troops were killed when their helicopter was shot down by a rocket-propelled grenade in the same area in 2005.

Concerns are also growing that Mr Bush wants to release fighting forces before he leaves office in January, in the event of conflict with Iran.

By the times of Mr Bush's departure, three of the 15 combat brigades now in Iraq could have left the country, say government and military officials. That would still leave up to 130,000 frontline troops in the field – a reduction from the 170,000 deployed in the "surge" last year.

A rapid US withdrawal would mark a sharp turnaround in the fortunes of the Bush administration from only two years ago, amid the bloody slaughter of growing numbers of Iraqis and American soldiers. Anti-war feeling is at fever pitch in the US and the military is said to be near breaking point from its extended combat deployments.

This was the climate in which Mr Obama, a fierce opponent of the war, shot to prominence to seek and eventually win the Democratic presidential nomination. The Illinois Senator will head to Baghdad in a few weeks to take soundings from Iraqi leaders and US military commanders about a withdrawal. He is taking with him the Republican Senator Chuck Hagel, a fierce critic of Mr Bush's policies in Iraq with him as he seeks to arrange the orderly removal of all US combat troops if he is elected president in November.

Mr Obama's plan is to remove one or two brigades every month, but he says that he will be guided by military commanders on the ground. Mr Hagel has sometimes been suggested as a possible vice-presidential running mate for Mr Obama, who needs to reach out to Republican voters if he is to expand the Democratic vote and win the White House. As the conditions in Iraq improve, the government and armed forces have shown an ability to combat insurgents that would have been unthinkable a short time ago. The number of attacks on American and other forces has dropped sharply and is now down to the levels of 2004 when the insurgency was gathering steam.

The faster pullout being considered by President Bush would free US troops for duties in Afghanistan where the Taliban and other insurgents are growing in confidence and strength. In the past three months more American soldiers died in Afghanistan than in Iraq as violence has declined.

"As the Iraqi security forces get stronger and get better, then we will be able to continue drawing down our troops in the future," the US Defence Secretary, Robert Gates, said last week.

General David Petraeus, the US commander in Iraq, is reviewing troop levels and officials say that he is expected to take a more cautions approach and recommend smaller reductions in forces.