Blair will also underline the need for the United States and Britain to “finish the job” both in Iraq and Afghanistan, so that the two countries are “transformed into nations of prosperity", added Foreign Office spokesman Michael O’Brien.
But the UK PM's scheduled address to a joint session of Congress in Washington has been clouded by an embarrassing rift over intelligence.
Blair said on Wednesday he stood behind the UK’s pre-war allegation that the former Iraqi president was seeking to buy uranium from Africa to revive a nuclear bomb programme - a charge the White House and the IAEA have both publicly disowned.
The US and UK sent over 250,000 troops to invade Iraq and based their case for war on Iraq's alleged weapons of mass destruction.
WMD allegations haunt US-UK axis
But both leaders have been accused of manipulating intelligence to justify attacking Iraq, a charge they deny.
Ten weeks after the war was declared over by Bush, no weapons have been found and a UK official told journalists last week it would be "extremely difficult" to uncover weapons which could prove their case.
About 146,000 US troops are in Iraq, facing a mounting resistance to their continued presence and dissatisfaction with the speed at which basic utilities are being restored.
After the latest grenade attack killed a US soldier on Wednesday, the official death toll of 147 has now equalled the number killed in the 1991 Gulf War, creating a shift in US public opinion and badly affecting troop morale.
Britain currently has 11,000 troops in Iraq. It officially suffered 33 fatalities during the war, and 10 more subsequently.
Critics of the Bush administration say it is keener on military action than the reconstruction that follows and a US election year is approaching, and point to Afghanistan as an example.
Britain has withdrawn over 30,000
troops since April
The British leader will also call on Bush to keep up pressure on Israelis and Palestinians to reach a lasting accord. "Terrorism cannot finally be defeated without one," he will say.
Poodle or partner
Blair's critics, who brand him Bush's "poodle", say the issue will show whether the British support for Iraq’s invasion and occupation can yield results.
His speech will make no reference to the nine Britons held in a military prison in Guantanamo Bay. Instead, officials said Blair and Bush may discuss the matter privately.
More than 200 British MPs who have called for Feroz Abbasi and Moazzam Begg, two of the British subjects facing trial in US military trbunals and possible death sentences, to be repatriated.
Both have been held in terrible conditions, presupposing guilt and the necessity to prove innocence.
O’Brien insisted the British PM would raise areas of disagreement with Bush, notably over the need to address climate change.
Bush has refused to sign up to the 1997 Kyoto treaty on cutting greenhouse gases, saying it would be too costly. The United States is the biggest emitter of greenhouse gases.