Bush puts his final stamp on Iraq as he promises to pull out just 8,000 troops - and plans 'quiet surge' in Afghanistan

But he was immediately blasted by Barack Obama, the man who hopes to succeed him in the White House, for delaying too long before sending more troops to Afghanistan, implying he would be ready to send promptly a much bigger force if elected.

Mr Bush argued that declining violence in Iraq allowed for a ‘quiet surge’ of troops to help combat the growing Taliban threat in Afghanistan.

Downsizing: George Bush waves after announcing his plans to withdraw 8,000 U.S. troops from Iraq

But Mr Obama claimed: ‘It is not enough troops, and not enough resources, with not enough urgency.’

The Democrat nominee said he would ‘finish the job’ in Afghanistan if he wins the White House election in November.

‘What President Bush and Senator McCain don’t understand is that the central front in the war on terror is not in Iraq, and it never was – the central front is in Afghanistan and Pakistan, where the terrorists who hit us on 9/11 are still plotting attacks seven years later,’ he added.

On patrol: American soldiers of 3rd Squadron, 3rd Armoured Cavalry Regiment patrol a road in Iraq's second largest city Mosul on Friday

In a speech at the National Defence University in Washington, Mr Bush said he would send another 4,500 troops to Afghanistan. He said the 146,000-strong US force in Iraq would be reduced by about 8,000 by February.

His critics have long argued that after invading Afghanistan one month after 9/11 the president should have ‘finished the job’ there, but was diverted to launching a war against Iraq in early 2003.

Democrats blasted Mr Bush for making strategic military decisions so close to the end of his presidency. He moves out of the White House in January, leaving his successor to decide on the future of both conflicts.

Handover: An Iraqi soldier mans a machinegun atop an armoured vehicle in Al Wahida district, south of Baghdad

Critics complained it was too little, too late from an administration that has allowed resurgent rebels to rise up in Afghanistan while it was sidetracked for years trying to deal with the violent aftermath of the ill-fated Iraq invasion.

‘I am stunned that President Bush has decided to bring so few troops home from Iraq and send so few resources to Afghanistan,’ said Senate Majority Leader Harry Reid.

‘As Democrats have been saying for years and as I saw with my own eyes last month, violence in Afghanistan has surged because Bush-McCain Republicans have all but ignored the true central front of the war on terror while keeping the bulk of our troops tied down in Iraq.’

The White House announcement returned national security to the top of the campaign agenda.

Mr Obama has advocated pulling all US combat forces out of Iraq within 16 months of taking office, while his Republican rival, John McCain, says he would rely on the advice of military commanders to determine the timing and pace of any troop reductions.

Both candidates have said reinforcements are needed in Afghanistan, to fight escalating violence.

The extra 4,500 troops heading to Afghanistan will be made up of a Marine battalion switched from its original deployment to Iraq in November and an Army combat brigade, increasing the US presence to 31,000.

‘For all the good work we have done in that country, it is clear we must do even more,’ said the president.

The scope and pace of the American troop withdrawals in Iraq are smaller than long anticipated, reflecting a desire by the military and the president not to jeopardise security gains.

‘Here is the bottom line: While the enemy in Iraq is still dangerous, we have seized the offensive, and Iraqi forces are becomingly increasingly capable of leading and winning the fight,’ added Mr Bush.

One Marine battalion, numbering about 1,000 troops, will go home as planned in November and not be replaced. An Army brigade of between 3,500 and 4,000 troops will leave in February.

Accompanying that combat drawdown will be the withdrawal of about 3,400 support forces over the next several months.