President Bush yesterday began an overhaul of his top military and diplomatic teams as he prepared to announce a highly controversial increase of 20,000 US troops in Iraq. He is to replace his two senior generals in Iraq, both said to be sceptical about increasing troop numbers, and he has also reshuffled his national security and foreign policy teams.

The moves are part of a broad mission to surround himself, both in Washington and on the ground in Iraq, with officials who support increasing troop numbers, a move largely opposed on Capitol Hill and among the American public.

Mr Bush is also beefing up his White House legal team in anticipation of a blizzard of Iraq-related subpoenas expected to be issued by the new Democrat-controlled Congress. On Thursday he accepted the resignation of Harriet Miers, his White House counsel, after aides expressed doubts about her ability to push back against what Democrats have promised will be vigorous oversight of the war’s management.

Mr Bush has also hired an extra four assistant White House counsel in recent weeks. Ms Miers’s position is expected to be filled by a heavyweight capable of resisting the looming Democrat onslaught.

As Mr Bush prepares to lay out his Iraq strategy to the nation next Wednesday night, he is set to confirm that General David Petraeus, who took part in the initial invasion, will replace General George Casey as the top ground commander.

Mr Bush also intends to endorse Admiral William Fallon to head US Central Command, replacing General John Abizaid as the top military commander for the Middle East. The choice of Admiral Fallon surprised some in the Pentagon as it would place a naval official with little experience of the Middle East in charge of two ground wars in Iraq and Afghanistan. But it also signalled a growing focus on the threat from Iran. Any mission against Tehran would rely heavily on carrier-based aircraft and missiles from the Persian Gulf. Generals Casey and Abizaid were deeply sceptical about increasing troop numbers in Iraq. General Petraeus supports a bigger US presence.

On the diplomatic side, Mr Bush is to name Ryan Crocker, a veteran diplomat who began his career in Iraq in the 1970s, as the new US ambassador in Baghdad. He will replace Zalmay Khalilzad, who moves from Baghdad to become the new US ambassador to the UN, replacing John Bolton.

Mr Bush yesterday presented a new intelligence chief, retired vice-admiral Mike McConnell. He will take over as director of national intelligence from John Negroponte, a former Iraqi ambassador, who is moving to the State Department as deputy to Condoleezza Rice. Admiral McConnell was a senior military intelligence official during the first Gulf War and ran the National Security Agency under Bill Clinton.

The US Army is stretched so thin that Mr Bush will rely heavily on extending tours in Iraq, and remobilising reserves, to make up his force “surge”.

He is also expected to send two additional army brigades, or roughly 7,000 soldiers, to Baghdad, and two Marine battalions, about 1,500 troops, to western Anbar Province, the heart of the Sunni insurgency.

The move comes amid continuing divisions between White House and Pentagon joint military chiefs about escalating troop numbers. The focus of the new mission will be to quell sectarian violence in Baghdad. But there are misgivings in the Administration about whether Nouri al-Maliki, Iraq’s Prime Minister, is capable of clamping down on the Shia militia, his political base. The undignified execution of Saddam Hussein has only reinforced the perception that Shia thugs control the country.

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