According to the Guardian newspaper, Blair interrupted a speech to a business group to say that in the wake of recent terrorist bombings in Turkey, Saudi Arabia and Iraq, "this is the right moment for us to stand firm with the United States in defeating terrorism wherever it is."
"Now is not the time to waver, now is the time to see it through," the prime minister said.
The president's impending arrival was bringing to a head widespread distrust of the American leader, the Iraq war, and the relationship between the White House and Downing Street — sentiments that posed the greatest political threat to Blair in his six years as prime minister.
To add to the tension for Blair's government, the former ambassador to the United States told a newspaper that Britain had warned the United States last autumn about troubles in postwar Iraq, but was ignored. Sir Christopher Meyer also tells The Observer Britain asked Mr. Bush to delay the start of war, but was rebuffed.
Children, lawmakers, peace activists, anarchists and at least one well-known American are all planning to join protests against Mr. Bush.
The rallies are expected to be loud, colorful — one plan is to pull down an effigy of Mr. Bush in Trafalgar Square in central London — and well-organized.
"This is the man who is in charge of the administration that's killed 8,000 Afghanis and 10,000 Iraqis," said Ghada Razuki of the Stop the War Coalition. "He is adding insult to injury by coming to our country and he's going to find out that he's not welcome."
Ron Kovic, the disabled U.S. Vietnam veteran and anti-war campaigner whose story was filmed as Born on the Fourth of July, led a coalition delegation to Blair's office Monday. They handed in a petition. said to bear more than 85,000 signatures, asking that Bush's invitation be revoked.
"We're going to stop this war (in Iraq) and change both of our countries. We're going to change the world," Kovic told reporters.
The coalition is hoping 60,000 people will join the main anti-Bush march through the city on Thursday. More than 3,000 "Stop Bush" placards have been printed.
The protesters appear to have support from a large section of the British public.
In a poll published last week, 59 percent of respondents said America's standing in the world has diminished under Mr. Bush's presidency, while 60 percent disapproved of his performance in Iraq. Forty-seven percent said Mr. Bush didn't seem up to the job of being U.S. president.
The Populus polling agency interviewed 964 adults by telephone between Nov. 7-9 for The Times survey. The margin of error was three percentage points.
The Stop the War Coalition was behind a huge anti-war rally in London in February. Up to 1 million Britons turned out to voice their opposition to the looming Iraq conflict.
Several other European anti-war groups have said they will travel to London for the protests, including France's Non a la Guerre (No to War), Italy's Ya Basta (Enough's Enough) and the Axis of Peace Coalition of France, Germany and Russia.
The rallies are also expected to attract hundreds of schoolchildren. "It is truanting for a good cause," said Verity Marriott, 16, who is organizing student "strikes."
The president says he understands why people oppose war.
"I understand particularly when I go and hug the moms and dads and brothers and sisters and sons and daughters of those who died," Monday's edition of The Sun newspaper in London quoted him as saying.
"I can also see the consequences of not acting, of hoping for the best in the face of tyrannical killers."
During his visit, the president will meet British leaders and the families of Britons killed in Afghanistan and Iraq. He will place a wreath at the Tomb of the Unknown Warrior.
The Metropolitan Police say they know of no specific security threat to Mr. Bush and his wife. A spokesman for the London force said Monday it was "monitoring activists who may be entering the U.K. in connection with President Bush's visit, but we're not prepared to discuss this further."
Sir John Stevens, who heads the Met, said security around the visit is unprecedented because of potential terrorism threats. Stevens has canceled holidays for all his London officers during Mr. Bush's visit and the security bill to the taxpayer is expected to top $4.7 million.
There's been criticism of some of the security plans for the visit, reports CBS News Correspondent Steve Holt. Anti-war demonstrators want to get close to the president with their protests, but the Secret Service has resisted. Scotland Yard is still trying to work out a compromise.