Six weeks before midterm elections in which the war is a crucial issue, the protest from the army head, General Peter Schoomaker, exposes concerns within the US military about the strain of the war on Iraq, and growing tensions between uniformed personnel and the Pentagon chief, Donald Rumsfeld.

Three retired senior military officers yesterday accused Mr Rumsfeld of bungling the war on Iraq, and said the Pentagon was "incompetent strategically, operationally and tactically". Major General Paul Eaton, a retired officer who was in charge of training Iraq troops, said: "Mr Rumsfeld and his immediate team must be replaced or we will see two more years of extraordinarily bad decision-making."

The rare criticism from the three officers, all veterans of the Iraq war, is an embarrassment to Mr Bush at a time when his party had hoped to campaign on its strong leadership in the "war on terror".

The officers echoed the findings of the National Intelligence Estimate at the weekend, which said the Iraq war had fuelled Islamist extremism around the world. They also accused the Pentagon of putting soldiers' lives at risk by failing to provide the best equipment available. "Why are we asking our soldiers and marines to use the same armour we found was insufficient in 2003?" asked Thomas Hammes, a retired Marine Corps colonel.

The criticism comes amid an unprecedented show of defiance from the army chief, Gen Schoomaker. The general refused to submit a budget plan for 2008 to Mr Rumsfeld, arguing the military could not continue operations in Iraq and its other missions without additional funds, the Los Angeles Times reported yesterday. The seriousness of the protest was underlined by Gen Schoomaker's reputation as an ally of the Pentagon chief. The general came out of retirement at Mr Rumsfeld's request to take up the post.

"It's quite a debacle," said Loren Thompson, a military analyst at the Lexington Institute thinktank. "Virtually everyone in the army feels as though their needs have been shortchanged."

Gen Schoomaker's defiance gives a voice to growing concern within the military about the costs of America's wars, and the long-term strain of carrying out operations around the world.

For the past three years, the $400bn (£210bn) cost of the wars in Iraq and Afghanistan have been funded by emergency spending bills passed by Congress. But Gen Schoomaker and others say the Iraq war has also put a severe strain on regular budgets. That puts the generals at odds with Mr Rumsfeld's strategic vision of a more nimble, hi-tech military. In addition, Congress and the White House have cut a number of army spending requests over the past months. "There is no sense in us submitting a budget that we can't execute, a broken budget," he told a Washington audience.

As the war in Iraq continues with no sign of a reduction in US forces, military officials have repeatedly complained about the strain on personnel, and say they fear they may be forced to rely more heavily on the National Guard and reservists to meet the demands of overseas deployments. General John Abizaid, America's senior commander in the Middle East, said last week there was little chance of any drawing down of the 140,000 forces in Iraq before next spring.

The burden of that commitment was underlined yesterday when the army extended the combat tours of about 4,000 soldiers serving in the Ramadi area.

In Basra yesterday, British troops killed a prominent al-Qaida figure who was hiding in Iraq after escaping from US custody in Afghanistan last year, the ministry of defence said. Omar Faruq was shot dead while resisting arrest during a pre-dawn raid by 250 soldiers after a long-planned intelligence-led operation. A British military spokesman described Faruq as a "very, very significant man".