By IAN BRUCE and MICHAEL SETTLE

THE senior US Democratic leader claimed last night that President George W Bush's decision to commit a further 21,500 US troops as a final gamble to stabilise Iraq left him "standing virtually alone".

Senator Harry Reid's attack on a White House policy adopted against the advice of military commanders and the Iraq Study Group's recommendations followed a poll yesterday which put approval of Bush's handling of the war at an all-time low of 29%.

Criticism also began to grow from Republicans who had until now backed Bush's strategies in the region.

Congressman Rik Keller, an ardent Bush supporter, said he would have agreed to boost US forces three years ago, but it was now "too late to solve an Iraqi political problem with an American military solution".

Bush, who said yesterday he had made mistakes in handling the war and the insurgency which followed, announced the "surge" reinforcement for Baghdad and neighbouring Anbar province.

He also demanded full co-operation from the Iraqi government and its total commitment to rooting out sectarian murder squads across the Sunni-Shia religious divide.

The president claimed the hard-line approach would help pull Iraq "out of its spiral of violence" and hasten the day when US troops could begin coming home.

More than 3000 American soldiers have died since the invasion to topple Saddam Hussein and 23,000 others have been wounded.

An increasingly war-weary and sceptical America yesterday heard Robert Gates, the Defence Secretary who replaced Donald Rumsfeld last month, say the surge was "temporary", then admit "no-one has a clear idea of how long that might be".

Asked if the planned US-Iraqi offensive to pacify Baghdad would target Moqtada al Sadr, the renegade Shi'ite cleric who commands up to 60,000 armed militiamen, Gates replied: "All lawbreakers are susceptible to being detained or taken care of in this campaign."

Al Sadr, a key political ally of Iraqi Prime Minister Nuri al Maliki, is head of the Mehdi Army, an Iranian-funded religious militia which runs parts of the capital. He is virulently anti-coalition and has already triggered an uprising against British and US troops in 2004.

British military sources said plans to begin reducing the 7200-strong UK garrison around Basra in the south this year were "very much dependent" on whether the planned US offensive in Baghdad stirred up a new wave of insurgency against coalition forces.

It followed reports that at least 3000 soldiers were to be withdrawn by May and all but a few hundred of the remaining British forces withdrawn to a desert base outside Basra to let Iraqi security forces assume control of the city.

The 600 British troops patrolling Maysan province, north-east of Basra, are also expected to be pulled back to a supporting role.

At Westminster, Des Browne, Defence Secretary, told MPs the government recognised a new battle for Baghdad could create a backlash in Basra province.

At a joint session of the defence and foreign affairs committees, he said: "If you disturb the Shia in Sadr City in Baghdad, will the Shia in Basra rise up in arms? We are well aware of that possibility."

Sir Jock Stirrup, Chief of the Defence Staff, accepted there was a "narrow window of opportunity" for the new US-led initiative to succeed.

Responding to a question about the controversial comment by General Sir Richard Dannatt, head of the Army, who claimed British troops "exacerbated" security problems in Iraq, Sir Jock suggested the longer UK forces stayed in Iraq the worse it would get, because the level of consent declined over time.