The Bush Administration was working hard today to persuade a sceptical America of the merits of President Bush's plan to salvage the mission to Iraq.

As dawn broke in Washington after the President's address to the nation last night, in which he announced that 21,500 extra soldiers would be sent to restore order to Baghdad and Anbar province, the White House despatched the Secretaries of State and Defence to woo Capitol Hill.

But in a sign of the political battle to come, they were met by noisy disapproval from the Democratic-controlled Congress as well as concerned members of Mr Bush's own Republican party. An AP-Ipsos poll showed that 70 per cent of Americans oppose sending more soldiers to Iraq.

"The President virtually stands alone," said Harry Reid, the Senate Majority Leader, while Chuck Hagel, a Republican Senator from Nebraska and a critic of the war, called Mr Bush's new plan "the most dangerous foreign policy blunder" since Vietnam.

The day before she leaves for a diplomatic visit to the Middle East, Condoleezza Rice spelled out her support for Mr Bush's strategy, which envisages a temporary surge of US forces to bring the violence in Baghdad under control, coupled with a marked handover of responsibility to the Iraqi government.

"Improvement in the security situation, especially in Baghdad, will open a window of opportunity for the Iraqi Government to accelerate the process of national reconciliation," she told the Senate Foreign Relations Committee. "We can and will measure whether this work is being done."

Like Mr Bush, Ms Rice repeatedly stressed that it was up to the Iraqi Prime Minister, Nouri al-Maliki, to lead the effort to contain the militias that are deepening the country's sectarian conflict.

But his ability to do so was the object of considerable scrutiny by Democratic Senators. Joe Biden, the chairman of the Senate Foreign Relations Committee, asked Ms Rice whether she really believed that Mr al-Maliki could stabilise the country.

"I think he knows that his government is in a sense on borrowed time," replied Dr Rice, only saying she was confident in Mr al-Maliki when asked a second time.

In Baghdad, the Prime Minister and his aides have been keen to present Mr Bush's plan as part of a wider Iraqi-led strategy to return order to the streets of the capital. Today a spokesman for Mr al-Maliki welcomed "the American commitment for success".

But other legislators were not so sure. "Sending more troops will not end the problem, on the contrary, there will be more bloodshed," said Hussein al-Falluji, a Sunni MP.

In the US Congress, Robert Gates, the recently installed Defence Secretary, voiced the Pentagon's approval for the plan.

Despite the advice of some military strategists, who have suggested that a "surge" of 21,500 troops is too small to make a significant difference to the violence in Iraq, Mr Gates sought to reassure Congress that the President has the backing of the military.

"Your senior professional military officers in Iraq and in Washington believe in the efficacy of the strategy outlined by the President last night," he told the House Armed Services Committee.

But Mr Gates swiftly encountered the scepticism of America's press and the gathering opposition of the Democrats. Asked at a news conference how long the extra deployment of US troops would last in Iraq, Mr Gates admitted he did not know. "It’s viewed as a temporary surge, but I think no one has a really clear idea of how long that might be," he said.

Ike Skelton, the Democratic chairman of the House Armed Services Committee, then described Mr Bush's plan as "three and a half years late and several hundred thousand troops short". Barack Obama, the Democratic Senator thought to be considering a run for the White House in 2008, said: "We’re not going to baby sit a civil war".

It was part of a morning of lively rhetoric in Washington, where the Democrats are thought to be exploring legislative means of expressing their disapproval of Mr Bush's plan without being drawn into a damaging fight with the White House in which they could be cast as failing to support the war effort.

Dick Durbin, a Democratic Senator from Illinois, said opposition to Mr Bush's plan was such that "questions are now being asked of this Administration that haven’t been asked for almost four years."

And resistance did not just fall along party lines. A handful of Republicans joined Mr Hagel to express their objections to Mr Bush's strategy and his refusal to accept more of the bipartisan recommendations of the Iraq Study Group.

Representative Ric Keller, a Republican and a former ardent supporter of the Bush Administration, said the plan to send more US troops to Iraq had come three years too late. "At this late stage, interjecting more young American troops into the crossfire of an Iraqi civil war is simply not the right approach," he said. "We are not going to solve an Iraqi political problem with an American military solution."

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